Ventricular assist device

ABSTRACT

Apparatus and methods are described including a left-ventricular assist device including an impeller and a frame disposed around the impeller. A pump-outlet tube traverses the subject&#39;s aortic valve with a distal portion of the pump-outlet tube disposed within the subject&#39;s left ventricle. The distal portion of the pump-outlet tube extends to a distal end of the frame and defines more than 10 blood-inlet openings that are sized such as (a) to allow blood to flow from the subject&#39;s left ventricle into the tube and (b) to block structures from the subject&#39;s left ventricle from entering into the frame. The porosity of the distal portion of the pump-outlet tube is lower within a proximal region of the distal portion of the pump-outlet tube than within a distal region of the distal portion of the pump-outlet tube that is distal to the proximal region. Other applications are also described.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.18/001,680 filed Dec. 13, 2022 to Tuval, which is a US national phaseapplication of PCT Application No. PCT/IB2022/051990 to Tuval (publishedas WO 22/189932), filed Mar. 7, 2022, which claims priority from:

U.S. Provisional Patent Application 63/158,708 to Tuval, entitled“Ventricular assist device,” filed Mar. 9, 2021, and

U.S. Provisional Patent Application 63/254,321 to Tuval, entitled“Ventricular assist device,” filed Oct. 11, 2021,

both of which US Provisional applications are incorporated herein byreference.

FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to medicalapparatus. Specifically, some applications of the present inventionrelate to a ventricular assist device and methods of use thereof.

BACKGROUND

Ventricular assist devices are mechanical circulatory support devicesdesigned to assist and unload cardiac chambers in order to maintain oraugment cardiac output. They are used in patients suffering from afailing heart and in patients at risk for deterioration of cardiacfunction during percutaneous coronary interventions. Most commonly, aleft-ventricular assist device is applied to a defective heart in orderto assist left-ventricular functioning. In some cases, aright-ventricular assist device is used in order to assistright-ventricular functioning. Such ventricular assist devices areeither designed to be permanently implanted or mounted on a catheter fortemporary placement.

SUMMARY OF EMBODIMENTS

In accordance with some applications of the present invention, aleft-ventricular assist device includes an impeller and a frame disposedaround the impeller. The frame includes strut junctions at a proximalend of the frame. The strut junctions are configured to be maintained inopen states, during assembly of the left ventricular assist device, tofacilitate insertion of the impeller into the frame. A securing elementholds the struts junctions in closed states, subsequent to the insertionof the impeller into the frame. A pump-outlet tube extends to a distalend of the frame and defines one or more lateral blood inlet openingsthat are configured to allow blood to flow from the subject's leftventricle into the pump-outlet tube.

For some applications (not shown), the pump-outlet tube defines two tofour lateral blood-inlet openings. Typically, for such applications,each of the blood-inlet openings defines an area of more than 20 squaremm (e.g., more than 30 square mm), and/or less than 60 square mm (e.g.,less than 50 square mm), e.g., 20-60 square mm, or 30-50 square mm.Alternatively or additionally, the outlet tube defines a greater numberof smaller blood-inlet openings 108, e.g., more than 10 blood-inletopenings, more than 50 blood-inlet openings, more than 100 blood-inletopenings, or more than 150 blood-inlet openings, e.g., 50-100blood-inlet openings, 100-150 blood-inlet openings, or 150-200blood-inlet openings. For some applications, the blood-inlet openingsare sized such as (a) to allow blood to flow from the subject's leftventricle into the tube and (b) to block structures from the subject'sleft ventricle from entering into the frame. Typically, for suchapplications, a distal conical portion of the pump-outlet tube (whichdefines the blood-inlet openings) is configured to reduce a risk ofstructures from the left ventricle (such as chordae tendineae,trabeculae carneae, and/or papillary muscles) entering into the frameand potentially being damaged by the impeller and/or the axial shaft,and/or causing damage to the left ventricular assist device.

Typically, the portion of the pump-outlet tube that defines theblood-inlet openings (e.g., the distal conical portion of thepump-outlet tube) has a porosity of more than 40 percent, e.g., morethan 50 percent, or more than 60 percent (where porosity is defined asthe percentage of the area of this portion that is porous to bloodflow). Thus, on the one hand, the blood-inlet openings are relativelysmall (in order to prevent structures of the left ventricular fromentering the frame), but on the other hand, the porosity of the portionof the pump-outlet tube that defines the blood-inlet openings isrelatively high, such as to allow sufficient blood flow into thepump-outlet tube.

For some applications, each the blood-inlet openings has a circular or apolygonal shape. For some applications, each of the blood-inlet openingshas a hexagonal shape. Typically, using openings having a hexagonalshape allows the portion of the pump-outlet tube that defines theblood-inlet openings to have a relatively high porosity (e.g., asdescribed hereinabove), while providing the portion of the pump-outlettube that defines the blood-inlet openings with sufficient materialbetween the blood-inlet openings to prevent tearing and/or stretching ofthe material.

For some applications, within a proximal region of the distal conicalportion of the pump-outlet tube (which typically defines the blood-inletopenings), the widths of the gaps between the hexagonal (or other typeof polygonal) holes are larger than widths of the gaps between thehexagonal (or other type of polygonal) holes within a distal region ofthe distal conical portion of the pump-outlet tube. Typically, for suchapplications, within the proximal region of the distal conical portionof the pump-outlet tube, a distance between opposing sides of each ofthe hexagons (or other type of polygons) is smaller than the distancebetween opposing sides of each of the hexagons (or other type ofpolygons) within the distal region of the distal conical portion of thepump-outlet tube. (Typically, such distances also represent the diameterof a circle that is enclosed by the respectively sized polygons.)Further typically, within the distal region of the distal conicalportion of the pump-outlet tube, the distal conical portion ofpump-outlet tube, has a higher porosity than within the proximal regionof the distal conical portion of the pump-outlet tube.

Typically, the pump-outlet tube is coupled to the frame via heating. Forsome applications, within the proximal region of the distal conicalportion of the pump-outlet tube, the gaps between the blood-inlet holesare wider and/or the blood-inlet holes are smaller than within thedistal region, and/or the porosity is lower than within the distalregion, in order to prevent and/or reduce damage (e.g., tearing,thinning, and/or stretching) that may be caused to the material thatdefines the blood-inlet holes from being damaged during theabove-described heating process.

For some applications, the ventricular assist device includes an innerlining that lines the inside of the frame that houses the impeller. Forsome applications, the inner lining is disposed inside the frame, inorder to provide a smooth inner surface (e.g., a smooth inner surfacehaving a substantially circular cross-sectional shape) through whichblood is pumped by impeller. Typically, by providing a smooth surface,the covering material reduces hemolysis that is caused by the pumping ofblood by the impeller, relative to if the blood were pumped between theimpeller and struts of the frame. For some applications, inner liningincludes polyurethane, polyester, and/or silicone. Alternatively oradditionally, the inner lining includes polyethylene terephthalate (PET)and/or polyether block amide (PEBAX®).

Typically, over an area of overlap between the inner lining and thepump-outlet tube, the inner lining is shaped to form a smooth surface(e.g., in order to reduce hemolysis, as described hereinabove), and thepump-outlet tube is shaped to conform with the struts of the frame.Further typically, the inner lining has a substantially circularcross-section. For some applications, over the area of overlap betweenthe inner lining and the pump-outlet tube, the pump-outlet tube and theinner lining are coupled to each other, e.g., via vacuum, via anadhesive, and/or using a thermoforming procedure, for example, asdescribed hereinbelow.

For some applications, the pump-outlet tube and the inner lining arebonded to each other and/or the frame in the following manner. For someapplications, the inner lining is directly bonded to the inner surfaceof the frame before the pump-outlet tube is bonded to the outside of theframe. It is noted that, by bonding the inner lining directly to theinner surface of the frame, (rather than simply bonding the inner liningto the pump-outlet tube and thereby sandwiching the frame between theinner lining to the pump-outlet tube), any air bubbles, folds, and otherdiscontinuities in the smoothness of the surface provided by the innerlining are typically avoided. For some applications, initially, theframe is treated so as to enhance bonding between the inner lining andthe inner surface of the frame. For some applications, the treatment ofthe frame includes applying a plasma treatment to the frame (e.g., tothe inner surface of the frame), dipping the frame in a coupling agentthat has at least two functional groups that are configured to bondrespectively with the frame and with the material form which the innerlining is made (e.g., silane solution), and/or dipping the frame in asolution that contains the material from which the inner lining is made(e.g., polyurethane solution). For some applications, subsequently, asolution that contains the material from which the inner lining is made(e.g., polyurethane solution) is sprayed over the central cylindricalportion of the cage. Once the inner surface of the frame has beentreated, the inner lining is bonded to the inner surface of the centralcylindrical portion of the frame (e.g., to the inner surface of acentral cylindrical portion of the frame). Typically, the inner lining(which is shaped as a tube), is placed over a mandrel, the frame isplaced over the inner lining, and pressure is applied by a heatshrinking process. Further typically, the assembly of the inner liningand the frame is heated in an oven.

Subsequent to the inner lining having been bonded to the frame, aportion of the pump-outlet tube is placed around the outside of theframe. Typically, the frame is heated from inside the frame, using themandrel. Typically, while the frame is heated, an outer tube (which istypically made from silicone) applies pressure to the pump-outlet tubethat causes pump-outlet tube to be pushed radially inwardly, in order tocause the pump-outlet tube to conform with the shapes of the struts ofthe frame. For some applications, during this stage, the mandrel that isplaced inside the inner lining and which heats the inner lining isshorter than the length of the inner lining. The mandrel is typicallyplaced within the inner lining such that margins are left outside of themandrel at each of the ends of the inner lining. Typically, the innerlining acts as a shield to protect the pump-outlet tube from beingoverheated and becoming damaged by the heating of the mandrel. Placingthe inner lining on the mandrel in the aforementioned manner preventsthe mandrel from coming into direct contact with the frame and/or thepump-outlet tube. For some applications, the combination of the frame,the inner lining, and the portion of the pump-outlet tube disposedaround the frame is subsequently shape set to a desired shape anddimensions using shape setting techniques as are known in the art.

Typically, the pump-outlet tube (or a different type of pump inletguard) includes a coupling portion (e.g., a tubular coupling portion, asshown), which extends distally from the pump-outlet tube. For someapplications, the coupling portion is coupled a surface that is distalto the frame in order to anchor the distal end of the pump-outlet tube.For some applications, the coupling portion defines a hole (e.g., towardthe distal end of the coupling portion). For some applications, adhesiveis applied between the coupling portion and the surface, via the hole.For some applications, the surface of is threaded. Typically, thethreaded surface allows the adhesive to gradually and uniformly spreadbetween the coupling portion and the surface. Further typically, thecoupling portion is transparent, such that the spread of the adhesive isvisible through the coupling portion. Therefore, for some applications,once the adhesive has sufficiently spread between the coupling portionand the surface (e.g., once the surface has been covered with theadhesive), application of the adhesive is terminated.

For some applications, the ventricular assist device including aprotective braid at a distal end thereof. For some applications, inorder to reduce a risk of structures from the left ventricle (such aschordae tendineae, trabeculae carneae, and/or papillary muscles)entering into the frame and potentially being damaged by the impellerand/or the axial shaft, and/or causing damage to the left ventricularassist device, the distal conical portion of the frame is covered(internally or externally) with the protective braid. Typically, withinat least a portion of the cylindrical portion of the frame, the braid isembedded between the pump-outlet tube and the inner lining, such that,during crimping of the frame, the braid becomes crimped with thepump-outlet tube and the inner lining, thereby preventing the braid frommoving with respect to pump-outlet tube and/or the inner lining.

In general, in the specification and in the claims of the presentapplication, the term “proximal” and related terms, when used withreference to a device or a portion thereof, should be interpreted tomean an end of the device or the portion thereof that, when insertedinto a subject's body, is typically closer to a location through whichthe device is inserted into the subject's body. The term “distal” andrelated terms, when used with reference to a device or a portionthereof, should be interpreted to mean an end of the device or theportion thereof that, when inserted into a subject's body, is typicallyfurther from the location through which the device is inserted into thesubject's body.

The scope of the present invention includes using the apparatus andmethods described herein in anatomical locations other than the leftventricle and the aorta. Therefore, the ventricular assist device and/orportions thereof are sometimes referred to herein (in the specificationand the claims) as a blood pump.

There is therefore provided, in accordance with some applications of thepresent invention, an apparatus including:

a left-ventricular assist device including:

-   -   an impeller configured to be placed inside a left ventricle of a        subject and to pump blood from the left ventricle to an aorta of        the subject, by rotating;    -   a frame disposed around the impeller, the frame including a        plurality of strut junctions at a proximal end of the frame, the        strut junctions being configured to be maintained in open        states, during assembly of the left ventricular assist device,        to facilitate insertion of the impeller into the frame;    -   a securing element configured to hold the struts junctions in        closed states, subsequent to the insertion of the impeller into        the frame; and    -   a pump-outlet tube configured to traverse an aortic valve of the        subject, such that a proximal portion of the pump-outlet tube is        disposed within the subject's aorta and a distal portion of the        pump-outlet tube is disposed within the subject's left        ventricle, the distal portion of the pump-outlet tube extending        to a distal end of the frame and defining one or more lateral        blood inlet openings that are configured to allow blood to flow        from the subject's left ventricle into the pump-outlet tube.

In some applications, the securing element includes a ring.

In some applications, the left-ventricular assist device includes aportion that is distal to the frame, and the pump-outlet tube furtherincludes a coupling portion that extends distally from the frame andthat is coupled to the portion of the left-ventricular assist devicethat is distal the frame.

In some applications, the distal portion of the pump-outlet tube definesmore than 10 blood-inlet openings that are sized such as (a) to allowblood to flow from the subject's left ventricle into the tube and (b) toblock structures from the subject's left ventricle from entering intothe frame. In some applications, the distal portion of the pump-outlettube defines more than 50 blood-inlet openings that are sized such as(a) to allow blood to flow from the subject's left ventricle into thetube and (b) to block structures from the subject's left ventricle fromentering into the frame.

In some applications, the left-ventricular assist device furtherincludes:

a proximal radial bearing disposed within a proximal bearing housing ata proximal end of the frame;

a distal radial bearing disposed within a distal bearing housing at adistal end of the frame;

an axial shaft upon which the impeller is disposed, the axial shaftpassing through the proximal radial bearing and the distal radialbearing,

the securing element is configured to hold the struts junctions closedaround an outer surface of the proximal bearing housing.

In some applications, the pump-outlet tube further includes a couplingportion that extends distally from the frame and that is coupled to thedistal bearing housing. In some applications, a distal end of the frameis coupled to an outer surface of the distal bearing housing. In someapplications, the left-ventricular assist device further includes adistal tip element, and the distal tip element is coupled to the distalbearing housing.

In some applications, the outer surface of the proximal bearing housingdefines grooves that are shaped to receive the strut junctions. In someapplications, the strut junctions define widened heads and the groovesare shaped to conform with the widened heads of the strut junctions.

In some applications, the proximal and distal radial bearings are madeof a ceramic material and the proximal and distal bearing housings aremade of a second material that is moldable into a desired shape. In someapplications, the proximal and distal bearing housings are made of ametal and/or an alloy. In some applications, the axial shaft includes ametal and/or an alloy and the axial shaft is covered with ceramicsleeves along regions of the axial shaft that come into contact witheither of the proximal and distal bearings during operation of theleft-ventricular assist device.

There is further provided, in accordance with some applications of thepresent invention, a method of manufacturing a left ventricular assistdevice, the method including:

forming a frame such that the frame is closed at its distal end and suchthat a plurality of strut junctions at a proximal end of the frame aremaintained in open states;

coupling a pump-outlet tube to the frame, such that a distal portion ofthe pump-outlet tube extends to a distal end of the frame and definesone or more lateral blood-inlet openings that are configured to allowblood to flow from the subject's left ventricle into the pump-outlettube, the pump-outlet tube being configured traverse an aortic valve ofa subject, such that a proximal portion of the pump-outlet tube isdisposed within the subject's aorta and the distal portion of thepump-outlet tube is disposed within the subject's left ventricle;

inserting an impeller into the frame via the proximal end of the frame,the impeller being configured to pump blood through the pump-outlettube, by rotating; and

subsequently, closing the strut junctions at the proximal and of theframe, and maintaining the strut junctions in their closed states usinga securing element.

In some applications, the pump-outlet tube further includes a couplingportion configured to extend distally from the frame, and the methodfurther includes coupling the coupling portion to a portion of theleft-ventricular assist device that is distal to the frame.

In some applications, the securing element includes a ring, andmaintaining the strut junctions in their closed states using thesecuring element includes maintaining the strut junctions in theirclosed states using the ring.

In some applications, the left-ventricular assist device furtherincludes:

a proximal radial bearing disposed within a proximal bearing housing ata proximal end of the frame;

a distal radial bearing disposed within a distal bearing housing at adistal end of the frame;

an axial shaft upon which the impeller is disposed, the axial shaftpassing through the proximal radial bearing and the distal radialbearing, and

maintaining the strut junctions in their closed states using thesecuring element includes maintaining the strut junctions in theirclosed states by holding the struts junctions closed around an outersurface of the proximal bearing housing.

In some applications, the pump-outlet tube further includes a couplingportion configured to extend distally from the frame, and the methodfurther includes coupling the coupling portion to the distal bearinghousing. In some applications, the method further includes coupling adistal end of the frame to an outer surface of the distal bearinghousing. In some applications, the method further includes coupling adistal tip element to the distal bearing housing.

In some applications, the outer surface of the proximal bearing housingdefines grooves that are shaped to receive the strut junctions, andholding the struts junctions closed around the outer surface of theproximal bearing housing includes holding the struts junctions withinthe grooves defined by the outer surface of the proximal bearinghousing. In some applications, the strut junctions define widened heads,and holding the struts junctions within the grooves defined by the outersurface of the proximal bearing housing includes holding the strutsjunctions within grooves that are shaped to conform with the widenedheads of the strut junctions.

In some applications, the proximal and distal radial bearings are madeof a ceramic material and the proximal and distal bearing housings aremade of a second material that is moldable into a desired shape. In someapplications, the proximal and distal bearing housings are made of ametal and/or an alloy. In some applications, the axial shaft includes ametal and/or an alloy and the method further includes covering the axialshaft with ceramic sleeves along regions of the axial shaft that comeinto contact with either of the proximal and distal bearings duringoperation of the left-ventricular assist device.

There is further provided, in accordance with some applications of thepresent invention, an apparatus, including:

a left-ventricular assist device including:

-   -   an impeller configured to be placed inside a left ventricle of a        subject and to pump blood from the left ventricle to an aorta of        the subject, by rotating;    -   a frame disposed around the impeller; and    -   a pump-outlet tube configured to traverse an aortic valve of the        subject, such that a proximal portion of the tube is disposed        within the subject's aorta and a distal portion of the        pump-outlet tube is disposed within the subject's left        ventricle,    -   the distal portion of the pump-outlet tube extending to a distal        end of the frame and defining more than 10 blood-inlet openings        that are sized such as (a) to allow blood to flow from the        subject's left ventricle into the tube and (b) to block        structures from the subject's left ventricle from entering into        the frame,    -   a porosity of the distal portion of the pump-outlet tube, which        defines the blood-inlet openings, is lower within a proximal        region of the distal portion of the pump-outlet tube than within        a distal region of the distal portion of the pump-outlet tube        that is distal to the proximal region.

In some applications, each of the blood-inlet openings is shaped suchthat, in at least one direction, a width of the opening is less than 1mm.

In some applications, a ratio of the porosity of the distal portion ofthe pump-outlet tube within the distal region to the porosity of thedistal portion of the pump-outlet tube within the proximal region ismore than 4:3.

In some applications, the porosity of the distal portion of thepump-outlet tube is varied between the proximal region and the distalregion such as to account for varying blood flow dynamics at differentregions of the distal portion of the pump-outlet tube. In someapplications, the distal portion of the pump-outlet tube is conical, andthe porosity of the distal portion of the pump-outlet tube is variedbetween the proximal region and the distal region such as to account forchanges in the shape of the distal conical portion along its length.

In some applications, along the distal region of the distal portion ofthe pump-outlet tube, the pump-outlet tube defines large blood-inletopenings that are configured to reduce a risk of thrombosis relative toif the blood-inlet openings along the distal region of the distalconical portion of the pump-outlet tube were smaller.

In some applications, the distal portion of the pump-outlet tube definesmore than 50 blood-inlet openings that are sized such as (a) to allowblood to flow from the subject's left ventricle into the tube and (b) toblock structures from the subject's left ventricle from entering intothe frame.

In some applications, the blood-inlet openings are rectangular and areshaped such that a ratio of lengths to widths of each of the blood-inletopenings is between 1.1:1 and 4:1. In some applications, the blood inletopenings are rectangular and are shaped such that a ratio of lengths towidths of each of the blood-inlet openings is between 3:2 and 5:2.

In some applications, the distal portion of the pump-outlet tube has aporosity of more than 40 percent. In some applications, the distalportion of the pump-outlet tube has a porosity of more than 50 percent.In some applications, the distal portion of the pump-outlet tube has aporosity of more than 60 percent.

In some applications, the frame defines a central cylindrical portionand a distal conical portion, the distal portion of the pump-outlettube, which defines the blood-inlet openings, is conical and is disposedover the distal conical portion of the frame, and a portion of thepump-outlet tube that is proximal to the distal portion of thepump-outlet tube is coupled to the central cylindrical portion of theframe.

In some applications, the portion of the pump-outlet tube that isproximal to the distal portion of the pump-outlet tube is coupled to thecentral cylindrical portion of the frame via heating, and the porosityis lower is within the proximal region of the distal portion of thepump-outlet tube, such that damage that may be caused to a material thatdefines the blood-inlet holes within the proximal region of the distalportion of the pump-outlet tube is reduced during the heating relativeto if the porosity within the proximal region of the distal portion ofthe pump-outlet tube was higher.

In some applications, the apparatus further includes an inner liningcoupled to an inner surface of the central cylindrical portion of theframe, such that the inner lining provides the central cylindricalportion of the frame with a smooth inner surface.

In some applications, the proximal region of the distal portion of thepump-outlet tube extends along a length of 0.5-2 mm.

In some applications, the blood-inlet openings have polygonal shapes. Insome applications, the blood-inlet openings have hexagonal shapes.

In some applications, within the proximal region of the distal portionof the pump-outlet tube, a diameter of a circle enclosed by each of theblood-inlet openings is between 0.1 and 0.6 mm. In some applications,within the proximal region of the distal portion of the pump-outlettube, widths of gaps between adjacent blood-inlet openings are between0.05 and 0.2 mm.

In some applications, within the distal region of the distal portion ofthe pump-outlet tube, a diameter of a circle enclosed by each of theblood-inlet openings is between 0.2 and 0.8 mm. In some applications,within the distal region of the distal portion of the pump-outlet tube,widths of gaps between adjacent blood-inlet openings are between 0.01 mmand 0.1 mm.

In some applications, a ratio of a diameter of a circle enclosed by eachthe blood-inlet openings with the distal region of the distal portion ofthe pump-outlet tube to a diameter of a circle enclosed by each of theblood-inlet openings with the proximal region of the distal portion ofthe pump-outlet tube is greater than 7:6. In some applications, a ratioof widths of gaps between adjacent blood-inlet openings with theproximal region of the proximal portion of the pump-outlet tube towidths of gaps between adjacent blood-inlet openings within the distalregion of the distal portion of the pump-outlet tube is greater than3:2.

There is further provided, in accordance with some applications of thepresent invention, a method, including:

manufacturing a housing for an impeller of a blood pump by:

-   -   treating a frame in order to enhance bonding between an inner        surface of the frame and an inner lining;    -   subsequently, coupling the inner lining to the inner surface of        the frame along at least a portion of a central cylindrical        portion of the frame, the central cylindrical portion of the        frame including struts that define a generally cylindrical        shape;    -   subsequent to coupling the inner lining to the inner surface of        the frame along at least a portion of the central cylindrical        portion of the frame:        -   placing a mandrel inside the inner lining;        -   placing a portion of an elongate tube around at least a            portion of the frame, the elongate tube including a proximal            portion that defines at least one blood outlet opening;        -   while the portion of the elongate tube is disposed around at            least the portion of the frame, heating the inner lining,            the frame and the portion of the elongate tube, via the            mandrel; and        -   while heating the inner lining, the frame, and the portion            of the elongate tube, applying pressure from outside the            portion of the elongate tube, such as to cause the portion            of the elongate tube to become coupled to the frame.

In some applications, struts of the central cylindrical portion of theframe define cells which are configured such that, in anon-radially-constrained configuration of the frame, a width of each ofeach of the cells within the central cylindrical portion of the frame asmeasured around a circumference of the central cylindrical portion ofthe frame is less than 2 mm.

In some applications, applying pressure from outside the portion of theelongate tube, while heating the inner lining, the frame and the portionof the elongate tube, includes causing the portion of the elongate tubeto conform with a structure of the struts of the frame.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of a central cylindrical portion ofthe frame includes coupling the inner lining to the inner surface of theframe along at least a portion of a central cylindrical portion of theframe, such that the inner lining has a substantially circular crosssection. In some applications, coupling the inner lining to the innersurface of the frame along at least a portion of a central cylindricalportion of the frame includes coupling the inner lining to the innersurface of the frame along at least a portion of a central cylindricalportion of the frame, such that the inner lining provides a smooth innersurface to the portion of the central cylindrical portion of the frameto which the inner lining is coupled.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of a central cylindrical portion ofthe frame includes avoiding air bubbles, folds, and otherdiscontinuities in smoothness of a surface provided by the inner lining.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesapplying a plasma treatment to the frame.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of a central cylindrical portion ofthe frame includes:

placing the inner lining over a mandrel;

placing the frame over the inner lining; and

applying pressure via a heat shrinking process.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesdipping the frame in a solution that contains the material from whichthe inner lining is made. In some applications, the inner liningincludes polyurethane and dipping the frame in the solution includesdipping the frame in a polyurethane solution.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesspraying the inner surface of the portion of the central cylindricalportion of the frame with a solution that contains the material fromwhich the inner lining is made. In some applications, the inner liningincludes polyurethane and spraying the inner surface of the portion ofthe central cylindrical portion of the frame includes spraying the innersurface of the portion of the central cylindrical portion of the framewith a polyurethane solution.

In some applications, placing the mandrel inside the inner liningsubsequent to coupling the inner lining to the inner surface of theframe along at least the portion of the central cylindrical portion ofthe frame includes placing a mandrel that is shorter than a length ofthe inner lining inside the inner lining. In some applications, placingthe mandrel inside the inner lining subsequent to coupling the innerlining to the inner surface of the frame along at least the portion ofthe central cylindrical portion of the frame includes placing themandrel within the inner lining such that margins are left outside ofthe mandrel at each end of the inner lining. In some applications,placing the mandrel within the inner lining such that margins are leftoutside of the mandrel at each end of the inner lining includespreventing the mandrel from coming into direct contact with the frame orthe pump-outlet tube, thereby protecting the pump-outlet tube from beingoverheated and becoming damaged by the heating of the mandrel.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesdipping the frame in a coupling agent that has at least two functionalgroups that are configured to bond respectively with the frame and witha material form which the inner lining is made. In some applications,the inner lining includes polyurethane and dipping the frame in thecoupling agent includes dipping the frame in the coupling agent includesdipping the frame in a silane solution.

There is further provided, in accordance with some applications of thepresent invention, a method, including:

manufacturing a housing for an impeller of a blood pump by:

-   -   placing a mandrel inside an inner lining, with a central        cylindrical portion of a frame disposed around the inner lining,        the central cylindrical portion of the frame including struts        that define a generally cylindrical shape,    -   the mandrel being shorter than a length of the inner lining;    -   placing a portion of an elongate tube around at least a portion        of the frame, the elongate tube including a proximal portion        that defines at least one blood outlet opening;    -   while the portion of the elongate tube is disposed around at        least the portion of the frame, heating the inner lining, the        frame and the portion of the elongate tube, via the mandrel; and    -   while heating the inner lining, the frame, and the portion of        the elongate tube, applying pressure from outside the portion of        the elongate tube, such as to cause the portion of the elongate        tube to become coupled to the frame.

In some applications, struts of the central cylindrical portion of theframe define cells which are configured such that, in anon-radially-constrained configuration of the frame, a width of each ofeach of the cells within the central cylindrical portion of the frame asmeasured around a circumference of the central cylindrical portion ofthe frame is less than 2 mm.

In some applications, applying pressure from outside the portion of theelongate tube, while heating the inner lining, the frame and the portionof the elongate tube, includes causing the portion of the elongate tubeto conform with a structure of the struts of the frame.

In some applications, placing the mandrel inside the inner liningincludes placing the mandrel within the inner lining such that marginsare left outside of the mandrel at each end of the inner lining. In someapplications, placing the mandrel within the inner lining such thatmargins are left outside of the mandrel at each end of the inner liningincludes preventing the mandrel from coming into direct contact with theframe or the pump-outlet tube, thereby protecting the pump-outlet tubefrom being overheated and becoming damaged by the heating of themandrel.

In some applications, the method further includes, prior to placing themandrel inside the inner lining:

treating the frame in order to enhance bonding between an inner surfaceof the frame and the inner lining; and

coupling the inner lining to the inner surface of the frame along atleast a portion of the central cylindrical portion of the frame.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of the central cylindrical portion ofthe frame includes coupling the inner lining to the inner surface of theframe along at least a portion of the central cylindrical portion of theframe, such that the inner lining has a substantially circular crosssection. In some applications, coupling the inner lining to the innersurface of the frame along at least a portion of the central cylindricalportion of the frame includes coupling the inner lining to the innersurface of the frame along at least a portion of the central cylindricalportion of the frame, such that the inner lining provides a smooth innersurface to the portion of the central cylindrical portion of the frameto which the inner lining is coupled.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of the central cylindrical portion ofthe frame includes avoiding air bubbles, folds, and otherdiscontinuities in a smoothness of a surface provided by the innerlining.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesapplying a plasma treatment to the frame.

In some applications, coupling the inner lining to the inner surface ofthe frame along at least a portion of a central cylindrical portion ofthe frame includes:

placing the inner lining over a mandrel;

placing the frame over the inner lining; and

applying pressure via a heat shrinking process.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesdipping the frame in a solution that contains the material from whichthe inner lining is made. In some applications, the inner liningincludes polyurethane and dipping the frame in the solution includesdipping the frame in a polyurethane solution.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesspraying the inner surface of the portion of the central cylindricalportion of the frame with a solution that contains the material fromwhich the inner lining is made. In some applications, the inner liningincludes polyurethane and spraying the inner surface of the portion ofthe central cylindrical portion of the frame includes spraying the innersurface of the portion of the central cylindrical portion of the framewith a polyurethane solution.

In some applications, treating the frame in order to enhance bondingbetween the inner surface of the frame and the inner lining includesdipping the frame in a coupling agent that has at least two functionalgroups that are configured to bond respectively with the frame and witha material form which the inner lining is made. In some applications,wherein the inner lining includes polyurethane and dipping the frame inthe coupling agent includes dipping the frame in the coupling agentincludes dipping the frame in a silane solution.

There is further provided, in accordance with some applications of thepresent invention, an apparatus including:

a left-ventricular assist device including:

-   -   an impeller configured to be placed inside a left ventricle of a        subject and to pump blood from the left ventricle to an aorta of        the subject, by rotating;    -   a frame disposed around the impeller, the frame defining a        distal conical portion;    -   a surface disposed distally to the frame; and    -   an inlet guard disposed over the distal conical portion of the        frame, the inlet guard:    -   defining blood-inlet openings that are sized such as (a) to        allow blood to flow from the subject's left ventricle into the        tube and (b) to block structures from the subject's left        ventricle from entering into the frame, and    -   a distal coupling portion, the distal coupling portion being        configured to be coupled to the surface that is disposed        distally to the frame, and the distal coupling portion defining        a hole which is configured to facilitate application of an        adhesive between the distal coupling portion and the surface        disposed distally to the frame.

In some applications, the inlet guard includes a distal portion of apump-outlet tube, the pump-outlet tube being configured to traverse anaortic valve of the subject, such that a proximal portion of thepump-outlet tube is disposed within the subject's aorta and the distalportion of the pump-outlet tube is disposed within the subject's leftventricle.

In some applications, the surface disposed distally to the frame isridged such as to enhance bonding between the surface and the couplingportion. In some applications, the surface disposed distally to theframe is threaded, such as to allow the adhesive to gradually anduniformly spread between the coupling portion and the surface.

In some applications, the coupling portion is tubular. In someapplications, the coupling portion is transparent such that spread ofadhesive between the coupling portion and the surface is visible.

In some applications, the left-ventricular assist device furtherincludes:

a proximal radial bearing disposed within a proximal bearing housing ata proximal end of the frame;

a distal radial bearing disposed within a distal bearing housing at adistal end of the frame;

an axial shaft upon which the impeller is disposed, the axial shaftpassing through the proximal radial bearing and the distal radialbearing,

the surface to which the distal coupling portion is coupled includes atleast a portion of an outer surface of the distal bearing housing.

In some applications, a distal end of the frame is coupled to a furtherportion of the outer surface of the distal bearing housing. In someapplications, the left-ventricular assist device further includes adistal tip element, and the distal tip element is coupled to a furtherportion of the outer surface of the distal bearing housing.

In some applications, a proximal end of the frame is coupled to an outersurface of the proximal bearing housing. In some applications, the frameincludes a plurality of strut junctions at a proximal end of the frame,the strut junctions being configured to be maintained in open states tofacilitate insertion of the impeller into the frame, during assembly ofthe left ventricular assist device, and the proximal end of the frame iscoupled to the outer surface of the proximal bearing housing by asecuring element holding the struts junctions in closed states aroundthe outer surface of the proximal bearing housing.

In some applications, the proximal and distal radial bearings are madeof a ceramic material and the proximal and distal bearing housings aremade of a second material that is moldable into a desired shape. In someapplications, the proximal and distal bearing housings are made of ametal and/or an alloy. In some applications, the axial shaft includes ametal and/or an alloy and the axial shaft is covered with ceramicsleeves along regions of the axial shaft that come into contact witheither of the proximal and distal bearings during operation of theleft-ventricular assist device.

There is further provided, in accordance with some applications of thepresent invention, an apparatus, including:

a ventricular assist device including:

-   -   a frame including struts that define a plurality of cells, the        frame being configured such that, in a non-radially-constrained        configuration of the frame, the frame includes a generally        cylindrical central portion;    -   a pump-outlet tube that defines one or more blood outlet        openings, a portion of the pump-outlet tube being disposed        outside the frame and coupled to the generally cylindrical        central portion of the frame, such that the portion of the        pump-outlet tube conforms with a structure of struts of the        frame;    -   an inner lining coupled to an inside of the generally        cylindrical central portion of the frame, such as to provide the        generally cylindrical portion of the frame with a smooth inner        surface;    -   an impeller disposed at least partially inside the generally        cylindrical central portion of the frame and configured to pump        blood through the tube and out of the one of more blood outlet        openings; and    -   a protective braid disposed over a distal portion of the frame        and configured to block structures from the subject's left        ventricle from entering into the frame,    -   a proximal end of the protective braid being embedded between        the pump-outlet tube and the inner lining, such that, during        crimping of the frame, the braid becomes crimped with the        pump-outlet tube and the inner lining, thereby preventing the        braid from moving with respect to pump-outlet tube or the inner        lining.

In some applications, the braid is woven into struts of the distalportion of frame.

In some applications, the distal portion of the frame is conical, andthe protective braid extends until the end of the distal conical portionof the frame.

In some applications, the braid is covered along a distal part of thedistal conical portion of the frame, in order to prevent thrombi fromforming on the braid within the distal part of the distal conicalportion of the frame.

In some applications, within a distal part of the distal conical portionof the frame, the braid is opened such as to define large apertures, inorder to prevent thrombi from forming on the braid within the distalpart of the distal conical portion of the frame. In some applications,within a distal part of the distal conical portion of the frame, thebraid is cut such as to define large apertures, in order to preventthrombi from forming on the braid within the distal part of the distalconical portion of the frame.

In some applications, the braid is covered along a distal part of thedistal conical portion of the frame, and the covered braid is cut suchas to define one or more large apertures, in order to prevent thrombifrom forming on the braid within the distal part of the distal conicalportion of the frame. In some applications, an aperture is cut from thecovered braid around the full circumference of the frame, such that thatthe covered braid defines an aperture that extends around the fullcircumference of the distal part of the distal conical portion of theframe. In some applications, the aperture is cut such that it extendsuntil a distal end of the distal conical portion of the frame, such thatthere is a single aperture that extends around the full circumference ofthe frame and until the distal end of the distal conical portion of theframe.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are schematic illustrations of a ventricular assistdevice, a distal end of which is configured to be placed in a subject'sleft ventricle, in accordance with some applications of the presentinvention;

FIG. 2 is a schematic illustration of a frame that houses an impeller ofa ventricular assist device, in accordance with some applications of thepresent invention;

FIGS. 3A, 3B, 3C, 3D, and 3E are schematic illustrations of an impellerof a ventricular assist device or portions thereof, in accordance withsome applications of the present invention;

FIG. 4 is a schematic illustration of an impeller disposed inside aframe of a ventricular assist device, in accordance with someapplications of the present invention;

FIGS. 5A and 5B are schematic illustrations of the impeller and theframe of the ventricular assist device, respectively innon-radially-constrained and radially-constrained states thereof, inaccordance with some applications of the present invention;

FIGS. 6A and 6B are schematic illustrations of a ventricular assistdevice at respective stages of a motion cycle of the impeller of theventricular assist device with respect to the frame of the ventricularassist device, in accordance with some applications of the presentinvention;

FIG. 7 is a schematic illustration of a motor unit of a ventricularassist device, in accordance with some applications of the presentinvention;

FIGS. 8A and 8B are schematic illustrations of a motor unit of aventricular assist device, in accordance with some applications of thepresent invention;

FIGS. 9A and 9B are schematic illustrations of a ventricular assistdevice that includes an inner lining on the inside of the frame thathouses the impeller, in accordance with some applications of the presentinvention;

FIGS. 10A, 10B, and 10C are schematic illustrations of a frame of aventricular assist device that includes a protective braid at a distalend thereof, in accordance with some applications of the presentinvention;

FIGS. 11A, 11B, 11C, and 11D are schematic illustrations of apump-outlet tube that defines blood-inlet openings at a distal endthereof, in accordance with some applications of the present invention;and

FIGS. 12A and 12B are schematic illustrations of a pump-outlet tube thatdefines blood-inlet openings at a distal end thereof, in accordance withsome applications of the present invention;

FIGS. 13A and 13B are schematic illustrations of a pump-outlet tube thatdefines blood-inlet openings at a distal end thereof, in accordance withsome applications of the present invention;

FIGS. 14A and 14B are schematic illustrations of a frame of aventricular assist device that includes a protective braid at a proximalend thereof, in accordance with some applications of the presentinvention; and

FIG. 15 is a schematic illustration of a pump-outlet tube that definesblood-outlet openings at a proximal end thereof, in accordance with someapplications of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIGS. 1A, 1B, and 1C, which are schematicillustrations of a ventricular assist device 20, a distal end of whichis configured to be disposed in a subject's left ventricle 22, inaccordance with some applications of the present invention. FIG. 1Ashows an overview of the ventricular assist device system including acontrol console 21, and a motor unit 23, FIG. 1B shows the ventricularassist device being inserted into the subject's left ventricle, and FIG.1C shows a pump-head portion 27 of the ventricular assist device ingreater detail. The ventricular assist device includes a pump-outlettube 24, which traverses an aortic valve 26 of the subject, such that aproximal end 28 of the pump-outlet tube is disposed in an aorta 30 ofthe subject and a distal end 32 of the pump-outlet tube is disposedwithin left ventricle 22. Pump-outlet tube 24 (which is sometimesreferred to herein as a “blood-pump tube”) is typically an elongatetube, an axial length of the pump-outlet tube typically beingsubstantially larger than its diameter. The scope of the presentinvention includes using the apparatus and methods described herein inanatomical locations other than the left ventricle and the aorta.Therefore, the ventricular assist device and/or portions thereof aresometimes referred to herein (in the specification and the claims) as ablood pump.

For some applications, the ventricular assist device is used to assistthe functioning of a subject's left ventricle during a percutaneouscoronary intervention. In such cases, the ventricular assist device istypically used for a period of up to six hours (e.g., up to ten hours),during a period in which there is risk of developing hemodynamicinstability (e.g., during or immediately following the percutaneouscoronary intervention). Alternatively or additionally, the ventricularassist device is used to assist the functioning of a subject's leftventricle for a longer period (e.g., for example, 2-20 days, e.g., 4-14days) upon a patient suffering from cardiogenic shock, which may includeany low-cardiac-output state (e.g., acute myocardial infarction,myocarditis, cardiomyopathy, post-partum, etc.). For some applications,the ventricular assist device is used to assist the functioning of asubject's left ventricle for yet a longer period (e.g., several weeks ormonths), e.g., in a “bridge to recovery” treatment. For some suchapplications, the ventricular assist device is permanently orsemi-permanently implanted, and the impeller of the ventricular assistdevice is powered transcutaneously, e.g., using an external antenna thatis magnetically coupled to the impeller.

As shown in FIG. 1B, which shows steps in the deployment of theventricular assist device in the left ventricle, typically the distalend of the ventricular assist device is guided to the left ventricleover a guidewire 10. During the insertion of the distal end of thedevice to the left ventricle, a delivery catheter 143 is disposed overthe distal end of the device. Once the distal end of the device isdisposed in the left ventricle, the delivery catheter is typicallyretracted to the aorta, and the guidewire is withdrawn from thesubject's body. The retraction of the delivery catheter typically causesself-expandable components of the distal end of the device to assumenon-radially-constrained configurations, as described in further detailhereinbelow. Typically, the ventricular assist device is inserted intothe subject's body in order to provide an acute treatment to thesubject. For some applications, in order to withdraw the leftventricular device from the subject's body at the end of the treatment,the delivery catheter is advanced over the distal end of the device,which causes the self-expandable components of the distal end of thedevice to assume radially-constrained configurations. Alternatively oradditionally, the distal end of the device is retracted into thedelivery catheter which causes the self-expandable components of thedistal end of the device to assume radially-constrained configurations.

For some applications (not shown), the ventricular assist device and/ordelivery catheter 143 includes an ultrasound transducer at its distalend and the ventricular assist device is advanced toward the subject'sventricle under ultrasound guidance.

Reference is made to FIG. 1C, which shows pump-head portion 27 ofventricular assist device 20, in accordance with some applications ofthe present invention, in greater detail. Typically, an impeller 50 isdisposed within a distal portion 102 of pump-outlet tube 24 and isconfigured to pump blood from the left ventricle into the aorta byrotating. The pump-outlet tube typically defines one or more blood-inletopenings 108 at the distal end of the pump-outlet tube, via which bloodflows into the pump-outlet tube from the left ventricle, duringoperation of the impeller. As shown in FIG. 1C, for some applications,the pump-outlet tube defines a single axially-facing blood-inletopening. Alternatively, the pump-outlet tube defines a plurality oflateral blood-inlet openings (e.g., as shown in FIG. 1B), as describedin further detail hereinbelow. For some applications, proximal portion106 of the pump-outlet tube defines one or more blood-outlet openings109, via which blood flows from the pump-outlet tube into the ascendingaorta, during operation of the impeller.

For some applications, control console 21 (shown in FIG. 1A), whichtypically includes a computer processor 25, drives the impeller torotate. For example, the computer processor may control a motor 74(shown in FIG. 7 ), which is disposed within motor unit 23 (shown inFIG. 1A) and which drives the impeller to rotate via a drive cable 130(shown in FIG. 7 ). For some applications, the computer processor isconfigured to detect a physiological parameter of the subject (such asleft-ventricular pressure, cardiac afterload, rate of change ofleft-ventricular pressure, etc.) and to control rotation of the impellerin response thereto, as described in further detail hereinbelow.Typically, the operations described herein that are performed by thecomputer processor, transform the physical state of a memory, which is areal physical article that is in communication with the computerprocessor, to have a different magnetic polarity, electrical charge, orthe like, depending on the technology of the memory that is used.Computer processor 25 is typically a hardware device programmed withcomputer program instructions to produce a special-purpose computer. Forexample, when programmed to perform the techniques described herein,computer processor 25 typically acts as a special-purpose,ventricular-assist computer processor and/or a special-purpose,blood-pump computer processor.

For some applications, a purging system 29 (shown in FIG. 1A) drives afluid (e.g., a glucose solution) to pass through portions of ventricularassist device 20, for example, in order to cool portions of the device,to purge and/or lubricate interfaces between rotating parts andstationary bearings, and/or in order to wash debris from portions of thedevice.

Typically, along distal portion 102 of pump-outlet tube 24, a frame 34is disposed within the pump-outlet tube around impeller 50. The frame istypically made of a shape-memory alloy, such as nitinol. For someapplications, the shape-memory alloy of the frame is shape set such thatat least a portion of the frame (and thereby distal portion 102 of tube24) assumes a generally circular, elliptical, or polygonalcross-sectional shape in the absence of any forces being applied todistal portion 102 of tube 24. By assuming its generally circular,elliptical, or polygonal cross-sectional shape, the frame is configuredto hold the distal portion of the pump-outlet tube in an open state.Typically, during operation of the ventricular assist device, the distalportion of the pump-outlet tube is configured to be placed within thesubject's body, such that the distal portion of the pump-outlet tube isdisposed at least partially within the left ventricle.

For some applications, along proximal portion 106 of pump-outlet tube24, the frame is not disposed within the pump-outlet tube, and thepump-outlet tube is therefore not supported in an open state by frame34. Pump-outlet tube 24 is typically made of a blood-impermeablecollapsible material. For example, pump-outlet tube 24 may includepolyurethane, polyester, and/or silicone. Alternatively or additionally,the pump-outlet tube is made of polyethylene terephthalate (PET) and/orpolyether block amide (e.g., PEBAX®). For some applications (not shown),the pump-outlet tube is reinforced with a reinforcement structure, e.g.,a braided reinforcement structure, such as a braided nitinol tube.Typically, the proximal portion of the pump-outlet tube is configured tobe placed such that it is at least partially disposed within thesubject's ascending aorta. For some applications, the proximal portionof the pump-outlet tube traverses the subject's aortic valve, passingfrom the subject's left ventricle into the subject's ascending aorta, asshown in FIG. 1B.

As described hereinabove, the pump-outlet tube typically defines one ormore blood-inlet openings 108 at the distal end of the pump-outlet tube,via which blood flows into the pump-outlet tube from the left ventricle,during operation of the impeller. For some applications, the proximalportion of the pump-outlet tube defines one or more blood-outletopenings 109, via which blood flows from the pump-outlet tube into theascending aorta, during operation of the impeller. Typically, thepump-outlet tube defines a plurality of blood-outlet openings 109, forexample, between two and eight blood-outlet openings (e.g., between twoand four blood-outlet openings). During operation of the impeller, thepressure of the blood flow through the pump-outlet tube typicallymaintains the proximal portion of the tube in an open state. For someapplications, in the event that, for example, the impeller malfunctions,the proximal portion of the pump-outlet tube is configured to collapseinwardly, in response to pressure outside of the proximal portion of thepump-outlet tube exceeding pressure inside the proximal portion of thepump-outlet tube. In this manner, the proximal portion of thepump-outlet tube acts as a safety valve, preventing retrograde bloodflow into the left ventricle from the aorta.

Referring again to FIG. 1C, for some applications, frame 34 is shapedsuch that the frame defines a proximal conical portion 36, a centralcylindrical portion 38, and a distal conical portion 40. Typically, theproximal conical portion is proximally-facing, i.e., facing such thatthe narrow end of the cone is proximal with respect to the wide end ofthe cone. Further typically, the distal conical portion isdistally-facing, i.e., facing such that the narrow end of the cone isdistal with respect to the wide end of the cone. For some applications,pump-outlet tube 24 extends to the end of cylindrical portion 38 (orslightly proximal or distal thereof), such that the distal end of thepump-outlet tube defines a single axially-facing blood-inlet opening108, as shown in FIG. 1C. For some applications, within at least aportion of frame 34 (e.g., along all of, or a portion of, the centralcylindrical portion of the frame), an inner lining 39 lines the frame.FIG. 1C shows an embodiment of the pump-head portion without innerlining 39, but several figures (e.g., FIGS. 4, 5A, 6A-6B, 9A-9B,10A-10C, 11A, 11C, 13A, and 14A-C) show embodiments of a pump-headportion that includes inner lining 39. In accordance with respectiveapplications, the inner lining partially overlaps or fully overlaps withpump-outlet tube 24 over the portion of the frame that the inner lininglines, as described in further detail hereinbelow with reference toFIGS. 9A-B.

Typically, pump-outlet tube 24 includes a conical proximal portion 42and a cylindrical central portion 44. The proximal conical portion istypically proximally-facing, i.e., facing such that the narrow end ofthe cone is proximal with respect to the wide end of the cone.Typically, blood-outlet openings 109 are defined by pump-outlet tube 24,such that the openings extend at least partially along the proximalconical section of tube 24. For some such applications, the blood-outletopenings are teardrop-shaped, as shown in FIG. 1C. Typically, theteardrop-shaped nature of the blood-outlet openings in combination withthe openings extending at least partially along the proximal conicalsection of tube 24 causes blood to flow out of the blood-outlet openingsalong flow lines that are substantially parallel with the longitudinalaxis of tube 24 at the location of the blood-outlet openings.

For some applications (not shown), the diameter of pump-outlet tube 24changes along the length of the central portion of the pump-outlet tube,such that the central portion of the pump-outlet tube has afrustoconical shape. For example, the central portion of the pump-outlettube may widen from its proximal end to is distal end, or may narrowfrom its proximal end to its distal end. For some applications, at itsproximal end, the central portion of the pump-outlet tube has a diameterof between 5 and 7 mm, and at its distal end, the central portion of thepump-outlet tube has a diameter of between 8 and 12 mm.

Again referring to FIG. 1C, the ventricular assist device typicallyincludes a distal-tip element 107 that is disposed distally with respectto frame 34 and that includes an axial-shaft-receiving tube 126 and adistal-tip portion 120. Typically, the axial-shaft receiving tube isconfigured to receive a distal portion of an axial shaft 92 of thepump-head portion during axial back-and-forth motion of the axial shaft(as described in further detail hereinbelow), and/or during delivery ofthe ventricular assist device. (Typically, during delivery of theventricular assist device, the frame is maintained in aradially-constrained configuration, which typically causes the axialshaft to be disposed in a different position with respect to the framerelative to its disposition with respect to the frame during operationof the ventricular assist device). Typically, distal-tip portion 120 isconfigured to assume a curved shape upon being deployed within thesubject's left ventricle, e.g., as shown in FIG. 1C. For someapplications, the curvature of the distal-tip portion is configured toprovide an atraumatic tip to ventricular assist device 20. Alternativelyor additionally, the distal-tip portion is configured to spaceblood-inlet openings 108 of the ventricular assist device from walls ofthe left ventricle.

As shown in the enlarged portion of FIG. 1B, for some applications,pump-outlet tube 24 extends to the end of distal conical portion 40 ofthe frame, and the pump-outlet tube defines a plurality of lateralblood-inlet openings 108, as described in further detail hereinbelow.For such applications, the pump-outlet tube typically defines a distalconical portion that is distally facing, i.e., such that the narrow endof the cone is distal with respect to the wide end of the cone. For somesuch applications (not shown), the pump-outlet tube defines two to fourlateral blood-inlet openings (e.g., four lateral blood-inlet openings,as shown). Typically, for such applications, each of the blood-inletopenings defines an area of more than 20 square mm (e.g., more than 30square mm), and/or less than 60 square mm (e.g., less than 50 squaremm), e.g., 20-60 square mm, or 30-50 square mm. Alternatively oradditionally, the outlet tube defines a greater number of smallerlateral blood-inlet openings, e.g., more than 10 blood-inlet openings,more than 50 blood-inlet openings, more than 200 blood-inlet openings,or more than 400 blood-inlet openings, e.g., 50-100 blood-inletopenings, 100-400 blood-inlet openings, or 400-600 blood-inlet openings.For some such applications, each of the blood-inlet openings defines anarea of more than 0.05 square mm (e.g., more than 0.1 square mm), and/orless than 3 square mm (e.g., less than 1 square mm), e.g., 0.05-3 squaremm, or 0.1-1 square mm. Alternatively, each of the blood-inlet openingsdefines an area of more than 0.1 square mm (e.g., more than 0.3 squaremm), and/or less than 5 square mm (e.g., less than 1 square mm), e.g.,0.1-5 square mm, or 0.3-1 square mm.

Reference is now made to FIG. 2 , which is schematic illustration offrame 34 that houses an impeller of ventricular assist device 20, inaccordance with some applications of the present invention. Frame 34 istypically made of a shape-memory alloy, such as nitinol, and theshape-memory alloy of the frame is shape set such that the centralportion of the frame (and thereby tube 24) assumes a generally circular,elliptical, or polygonal cross-sectional shape in the absence of anyforces being applied to pump-outlet tube 24. By assuming its generallycircular, elliptical, or polygonal cross-sectional shape, the frame isconfigured to hold the distal portion of the tube in an open state.

Typically, the frame is a stent-like frame, in that it comprises strutsthat, in turn, define cells. Further typically, the frame is coveredwith pump-outlet tube 24, and/or covered with an inner lining 39,described hereinbelow, with reference to FIGS. 9A-B. As describedhereinbelow, for some applications impeller 50 undergoes axialback-and-forth motion with respect to frame 34. Typically, over thecourse of the motion of the impeller with respect to the frame thelocation of the portion of the impeller that defines the maximum span ofthe impeller is disposed within central cylindrical portion 38 of frame34. In some cases, if the cells of the central cylindrical portion 38 offrame 34 are too large, then pump-outlet tube 24, and/or inner lining 39gets stretched between edges of the cells, such that the pump-outlettube 24, and/or inner lining 39 does not define a circularcross-section. For some applications, if this occurs in the region inwhich the portion of the impeller that defines the maximum span of theimpeller is disposed, this results in a non-constant gap between theedges of the impeller blades and tube 24 (and/or inner lining) at thatlocation, over the course of a rotation cycle of the impeller. For someapplications, this may lead to increased hemolysis relative to if therewere a constant gap between the edges of the impeller blades and tube 24(and/or inner lining) at that location, over the course of the rotationcycle of the impeller.

Referring to FIG. 2 , at least partially in view of the issues describedin the above paragraph, within central cylindrical portion 38 of frame34, the frame defines a large number of relatively small cells.Typically, when the frame is disposed in its non-radially-constrainedconfiguration, the maximum cell width CW of the each of the cells (i.e.,the distance from the inner edge of the strut at the central junction onone side of the cell to the inner edge of the strut at the centraljunction on the other side of the cell, as measured around thecircumference of cylindrical portion 38) within the cylindrical portionof the frame is less than 2 mm, e.g., between 1.4 mm and 1.6 mm, orbetween 1.6 and 1.8 mm. Since the cells are relatively small, innerlining 39 defines a substantially circular cross-section within thecylindrical portion of the frame.

Still referring to FIG. 2 , and starting from the distal end of theframe (which is to the right of the figure), typically the frame definesthe following portions (a) coupling portion 31 via which the frame iscoupled to a distal bearing housing 118H (shown in FIG. 5A) of theventricular assist device, (b) distal conical portion 40, (c) centralcylindrical portion 38, (d) proximal conical portion 36, and (e)proximal strut junctions 33. As illustrated, as the frame transitionsfrom a proximal end of the frame toward the center of the frame (e.g.,as the frame transitions from proximal strut junctions 33, throughproximal conical portion 36, and to central cylindrical portion 38),struts 37 of the frame pass through junctions 35, at which the twostruts branch from a single strut, in a Y-shape. As described in furtherdetail hereinbelow, typically frame 34 is placed in aradially-constrained (i.e., crimped) configuration within deliverycatheter 143 by the frame being axially elongated. Moreover, the frametypically transmits its radial narrowing to the impeller, and theimpeller becomes radially constrained by becoming axially elongatedwithin the frame. For some applications, the struts of the frame beingconfigured in the manner described above facilitates transmission ofaxial elongation from the delivery catheter (or other device that isconfigured to crimp the frame) to the frame, which in turn facilitatestransmission of axial elongation to the impeller. This is because thepairs of struts that branch from each of junctions 35 are configured topivot about the junction and move closer to each other such as to close.

Still referring to FIG. 2 , during the assembly of the ventricularassist device, initially distal coupling portion 31 is coupled to adistal bearing housing 118H (shown in FIG. 5A), e.g., via a snap-fitmechanism. For some applications proximal strut junctions 33 are stillmaintained in open states at this stage, in order for the impeller to beplaced within the frame via the proximal end of the frame. Typically,the structure of frame 34 shown in FIG. 2 is used in applications inwhich pump-outlet tube extends to the distal end of frame 34 (e.g., asshown in FIG. 1B). In such cases, the impeller cannot be inserted viathe distal end of the frame, since the distal end of the frame iscovered by pump-outlet tube 24. During the assembly of the ventricularassist device, subsequent to the impeller being inserted via theproximal end of the frame, the proximal strut junctions are closed. Forsome applications, the proximal strut junctions are closed around theoutside of a proximal bearing housing 116H (shown in FIG. 5A), asdescribed in further detail hereinbelow with reference to FIGS. 5A-B.Typically, a securing element 117 (e.g., a ring shown in FIG. 5A) holdsthe strut junctions in their closed configurations around the outside ofproximal bearing housing 116H.

Typically, when disposed in its non-radially constrained configuration,frame 34 has a total length of more than 25 mm (e.g., more than 30 mm),and/or less than 50 mm (e.g., less than 45 mm), e.g., 25-50 mm, or 30-45mm. Typically, when disposed in its radially-constrained configuration(within delivery catheter 143), the length of the frame increases bybetween 2 and 5 mm. Typically, when disposed in its non-radiallyconstrained configuration, the central cylindrical portion of frame 34has a length of more than 10 mm (e.g., more than 12 mm), and/or lessthan 25 mm (e.g., less than 20 mm), e.g., 10-25 mm, or 12-20 mm. Forsome applications, a ratio of the length of the central cylindricalportion of the frame to the total length of the frame is more than 1:4and/or less than 1:2, e.g., between 1:4 and 1:2.

Reference is now made to FIGS. 3A-E, which are schematic illustrationsof impeller 50 or portions thereof, in accordance with some applicationsof the present invention. Typically, the impeller includes at least oneouter helical elongate element 52, which winds around a central axialspring 54, such that the helix defined by the helical elongate elementis coaxial with the central axial spring. Typically, the impellerincludes two or more helical elongate elements (e.g., three helicalelongate elements, as shown in FIGS. 3A-C). For some applications, thehelical elongate elements and the central axial spring are made of ashape-memory material, e.g., a shape-memory alloy, such as nitinol.Typically, each of the helical elongate elements and the central axialspring support a film 56 of a material (e.g., an elastomer, such aspolyurethane, and/or silicone) therebetween. For some applications, thefilm of material includes pieces of nitinol embedded therein, forexample in order to strengthen the film of material. For illustrativepurposes, the impeller is shown in the absence of the material in FIG.3A. FIGS. 3B and 3C show respective views of the impeller with thematerial supported between the helical elongate elements and the spring.FIGS. 3D and 3E show similar respective views of the impeller to thoseshown in FIGS. 3B and 3C, but with certain features of the impellerdiffering from those shown in FIGS. 3B and 3C, as elaborated uponhereinbelow.

Each of the helical elongate elements, together with the film extendingfrom the helical elongate element to the spring, defines a respectiveimpeller blade, with the helical elongate elements defining the outeredges of the blades, and the axial spring defining the axis of theimpeller. Typically, the film of material extends along and coats thespring. For some applications, sutures 53 (e.g., polyester sutures,shown in FIGS. 3A-C) are wound around the helical elongate elements.Typically, the sutures are configured to facilitate bonding between thefilm of material (which is typically an elastomer, such as polyurethane,or silicone) and the helical elongate element (which is typically ashape-memory alloy, such as nitinol). For some applications, sutures(e.g., polyester sutures, not shown) are wound around spring 54.Typically, the sutures are configured to facilitate bonding between thefilm of material (which is typically an elastomer, such as polyurethane,or silicone) and the spring (which is typically a shape-memory alloy,such as nitinol).

Typically, proximal ends of spring 54 and helical elongate elements 52extend from a proximal bushing (i.e., sleeve bearing) 64 of theimpeller, such that the proximal ends of spring 54 and helical elongateelements 52 are disposed at a similar radial distance from thelongitudinal axis of the impeller, as each other. Similarly, typically,distal ends of spring 54 and helical elongate elements 52 extend from adistal bushing 58 of the impeller, such that the distal ends of spring54 and helical elongate elements 52 are disposed at a similar radialdistance from the longitudinal axis of the impeller, as each other. Thehelical elongate elements typically rise gradually from the proximalbushing before reaching a maximum span and then falling gradually towardthe distal bushing. Typically, the helical elongate elements aresymmetrical along their lengths, such that the rising portions of theirlengths are symmetrical with respect to the falling portions of theirlengths. Typically, the impeller defines a lumen 62 therethrough (shownin FIG. 3C), with the lumen typically extending through, and beingdefined by, spring 54, as well as proximal bushing 64 and distal bushing58, of the impeller.

Reference is now made to FIG. 4 , which is a schematic illustration ofimpeller 50 disposed inside frame 34 of ventricular assist device 20, inaccordance with some applications of the present invention. For someapplications, within at least a portion of frame 34 (e.g., along all of,or a portion of, central cylindrical portion 38 of the frame), innerlining 39 lines the frame. In accordance with respective applications,the inner lining partially overlaps or fully overlaps with pump-outlettube 24 over the portion of the frame that the inner lining lines, asdescribed in further detail hereinbelow with reference to FIGS. 9A-B.

As shown in FIG. 4 , typically there is a gap G, between the outer edgeof impeller 50 and inner lining 39, even at a location at which the spanof the impeller is at its maximum. For some applications, it isdesirable that the gap between the outer edge of the blade of theimpeller and inner lining 39 be relatively small, in order for theimpeller to efficiently pump blood from the subject's left ventricleinto the subject's aorta. (It is noted that, by virtue of the relativelysmall gap between the outer edge of impeller 50 and inner lining 39 evenat a location at which the span of the impeller is at its maximum, aswell as the shape of the impeller, the impeller functions as anaxial-flow impeller, with the impeller pumping blood in the axialdirection from a distal end of pump-outlet tube 24 to the proximal endof the pump-outlet tube.) It is also desirable that a gap between theouter edge of the blade of the impeller and the inner surface of frame34 be maintained throughout the rotation of the impeller within frame34, for example, in order to reduce the risk of hemolysis.

For some applications, when impeller 50 and frame 34 are both disposedin non-radially-constrained configurations and prior to operation of theimpeller, gap G between the outer edge of the impeller and the innerlining 39, at the location at which the span of the impeller is at itsmaximum, is greater than 0.05 mm (e.g., greater than 0.1 mm), and/orless than 1 mm (e.g., less than 0.4 mm), e.g., 0.05-1 mm, or 0.1-0.4 mm.For some applications, when the impeller is disposed in itsnon-radially-constrained configurations and prior to operation of theimpeller, the outer diameter of the impeller at the location at whichthe outer diameter of the impeller is at its maximum is more than 7 mm(e.g., more than 8 mm), and/or less than 10 mm (e.g., less than 9 mm),e.g., 7-10 mm, or 8-9 mm. For some applications, when frame 34 isdisposed in its non-radially-constrained configuration, the innerdiameter of frame 34 (as measured from the inside of inner lining 39 onone side of the frame to the inside of inner lining on the opposite sideof the frame) is greater than 7.5 mm (e.g., greater than 8.5 mm), and/orless than 10.5 mm (e.g., less than 9.5 mm), e.g., 7.5-10.5 mm, or8.5-9.5 mm. For some applications, when the frame is disposed in itsnon-radially-constrained configuration, the outer diameter of frame 34is greater than 8 mm (e.g., greater than 9 mm), and/or less than 13 mm(e.g., less than 12 mm), e.g., 8-13 mm, or 9-12 mm.

Typically, an axial shaft 92 passes through the axis of impeller 50, vialumen 62 of the impeller. Further typically, the axial shaft is rigid,e.g., a rigid tube. For some applications, proximal bushing 64 of theimpeller is coupled to the shaft such that the axial position of theproximal bushing with respect to the shaft is fixed, and distal bushing58 of the impeller is slidable with respect to the shaft. For example,the proximal bushing may be coupled to a coupling element 65 disposed onthe axial shaft (shown in FIG. 4 ), for example via a snap-fitmechanism. (Alternatively, distal bushing 58 of the impeller is coupledto the shaft such that the axial position of the distal bushing withrespect to the shaft is fixed, and proximal bushing 64 of the impelleris slidable with respect to the shaft.) The axial shaft itself isradially stabilized via a proximal radial bearing 116 and a distalradial bearing 118. In turn, the axial shaft, by passing through lumen62 defined by the impeller, radially stabilizes the impeller withrespect to the inner surface of frame 34, such that even a relativelysmall gap between the outer edge of the blade of the impeller and theinner surface of frame 34 (e.g., a gap that is as described above) ismaintained, during rotation of the impeller.

Referring again to FIGS. 3A-C, for some applications, the impellerincludes a plurality of elongate elements 67 extending radially fromcentral axial spring 54 to outer helical elongate elements 52. Theelongate elements are typically flexible but are substantiallynon-stretchable along the axis defined by the elongate elements. Furthertypically, each of the elongate elements is configured not to exertforce upon the helical elongate element, unless force is acting upon theimpeller that is causing the helical elongate element to move radiallyoutward, such that (in the absence of the elongate element) a separationbetween the helical elongate element and the central axial spring wouldbe greater than a length of the elongate element. For example, theelongate elements may include strings (such as polyester, and/or anotherpolymer or a natural material that contains fibers) and/or wires (suchas nitinol wires, and/or wires made of a different alloy, or a metal).

For some applications, the elongate elements 67 maintain helicalelongate element 52 (which defines the outer edge of the impeller blade)within a given distance with respect to the central axial spring. Inthis manner, the elongate elements are configured to prevent the outeredge of the impeller from being forced radially outward due to forcesexerted upon the impeller during the rotation of the impeller. Theelongate elements are thereby configured to maintain the gap between theouter edge of the blade of the impeller and the inner surface of frame34, during rotation of the impeller. Typically, more than one (e.g.,more than two) and/or fewer than eight (e.g., fewer than four) elongateelements 67 are used in the impeller, with each of the elongate elementstypically being doubled (i.e., extending radially from central axialspring 54 to an outer helical elongate element 52, and then returningfrom the helical elongate element back to the central axial spring). Forsome applications, a plurality of elongate elements, each of whichextends from the spring to a respective helical elongate element andback to the spring, are formed from a single piece of string or a singlewire.

Reference is now made to FIGS. 3D and 3E, which are schematicillustrations of impeller 50, the impeller including a single integratedimpeller-overexpansion-prevention element 72 that defines a plurality ofelongate elements 67, in accordance with some applications of thepresent invention. For some applications,impeller-overexpansion-prevention element 72 (which defines a pluralityof elongate elements 67) is used as an alternative to elongate elements67 as shown in FIGS. 3A-C. For some applications, element 72 defines aring 73 and the plurality of elongate elements 67 extending radiallyfrom the ring. For some applications, rather than threading stringsand/or wire around spring 54, ring 73 of element 72 is placed around thespring, e.g., by being placed around tube 70, which is typicallydisposed at the longitudinally-central location of the spring. The endsof respective elongate elements 67 are then coupled to respectivehelical elongate elements 52. As described hereinabove, elongateelements 67 are typically flexible but are substantially non-stretchablealong the axis defined by the elongate elements. Further typically, eachof elongate elements 67 is configured to substantially not resistcompression. Rather, each elongate element 67 is configured to exert atensile force upon helical elongate element 52 that prevents helicalelongate element 52 from moving radially outward, such that (in theabsence of elongate element 67) a separation between helical elongateelement 52 and central axial spring 54 would be greater than a length ofelongate element 67. When a force is acting upon the impeller that wouldcause the helical elongate element 52 to move radially outward (in theabsence of elongate element 67), the impeller-overexpansion-preventionelement is configured to prevent radial expansion of the impeller.Typically, a respective elongate element 67 is disposed within each oneof the impeller blades and is configured to prevent the impeller bladefrom radially expanding. For some applications, element 72 is made ofpolyester, and/or another polymer or a natural material that containsfibers, and/or nitinol (or a similar shape-memory alloy).

It is noted that the scope of the present application includes usingsingle integrated impeller-overexpansion-prevention element 72 with animpeller having a different construction from that shown in FIGS. 3D-E.For example, the single integrated impeller-overexpansion-preventionelement 72 could be used with an impeller having a differentlyconstructed axial structure than spring 54. Typically, the axialstructure defines a lumen therethrough, such that the impeller defineslumen 62 therethrough.

For some applications, the following assembly technique is used tomanufacture the impeller while enhancing bonding of an elastomericmaterial that is used to form film 56 to the at least one helicalelongate element. Typically, bonding of the elastomeric material to theat least one helical elongate element is performed in a manner that doesnot cause a protrusion from the effective edge of the impeller blade.Further typically, bonding of the elastomeric material to the at leastone helical elongate element is performed in a manner that provides theimpeller blade with a rounded outer edge, by the elastomeric materialrounding edges of the helical elongate element. Proximal bushing 64,distal bushing 58, and helical elongate elements 52 are cut from a tubeof shape-memory material, such as nitinol. The cutting of the tube, aswell as the shape setting of the shape-memory material, is typicallyperformed such that the helical elongate elements and the bushings aredefined by a tube of shape-memory material that is cut and shape set.For some applications, prior to being coupled to spring 54, a plasmatreatment is applied to the helical elongate elements. Alternatively oradditionally, prior to being coupled to spring 54, the helical elongateelements are coated with a coupling agent. Typically, a coupling agentis selected that has at least two functional groups that are configuredto bond respectively with the helical elongate elements and with theelastomeric material. For example, a silane compound, such asn-(2-aminoethyl)-3-aminopropyltrimethoxysilane, may be used, with thesilane compound containing a first functional group (e.g., (OH)) whichis configured to bond with the helical elongate elements (which aretypically made of an alloy, such a nitinol), and the silane compoundcontaining a second functional group (e.g., (NH2)) which is configuredto bond with the elastomeric material. Typically, the functional groupsin the coupling agent are only active for a given time period (e.g.,approximately an hour or less). Therefore, during this time period, acoat of elastomeric material is applied around the helical elongateelements. Typically, the coat of elastomeric material is the sameelastomeric material or a similar elastomeric material to that used infilm 56. For example, a polycarbonate-based thermoplastic polyurethane,such as Aromatic Carbothane™ (e.g., Aromatic Carbothane™ 75A) may beused in film 56, and the coating may be the same polycarbonate-basedthermoplastic polyurethane, or a similar polycarbonate-basedthermoplastic polyurethane, such as Pellethane® (e.g., Pellethane® 90A).

As described hereinabove, proximal bushing 64, distal bushing 58, andhelical elongate elements 52 are typically cut from a tube ofshape-memory material, such as nitinol. For some applications,subsequent to the coating having been applied to the helical elongateelements 52, spring 54 is coupled to the helical elongate elements.Typically, spring 54 is inserted into the cut and shape-set tube, suchthat the spring extends along the length of the tube from at least theproximal bushing to the distal bushing. For some applications, thespring is inserted into the cut and shape-set tube while the spring isin an axially compressed state, and the spring is configured to be heldin position with respect to the tube, by exerting a radial force uponthe proximal and distal bushings. Alternatively or additionally,portions of the spring are welded to the proximal and distal bushings.For some applications, the spring is cut from a tube of a shape-memorymaterial, such as nitinol. For some such applications, the spring isconfigured such that, when the spring is disposed in anon-radially-constrained configuration (in which the spring is typicallydisposed during operation of the impeller), there are substantially nogaps between windings of the spring and adjacent windings thereto.

Typically, at this stage, overexpansion-prevention element 72 is placedbetween the spring and the helical elongate elements, as describedhereinabove, such that an assembly is formed that includes coatedhelical elongate elements 52, spring 54, and overexpansion-preventionelement 72.

For some applications, at this stage, the assembly of coated helicalelongate elements 52, spring 54, and overexpansion-prevention element72, is sprayed with a further layer of an elastomeric material.Typically, the elastomeric material that is sprayed is the sameelastomeric material or a similar elastomeric material to that used asfilm 56. For example, a polycarbonate-based thermoplastic polyurethane,such as Aromatic Carbothane™ (e.g., Aromatic Carbothane™ 75A) may beused as film 56, and the sprayed material may be the samepolycarbonate-based thermoplastic polyurethane, or a similarpolycarbonate-based thermoplastic polyurethane, such as Pellethane®(e.g., Pellethane® 90A). For some applications, applying the spray tothe helical elongate elements rounds the helical elongate elements.Typically, when the helical elongate element has a rounded crosssection, the elastomeric material forms a layer having a substantiallyuniform thickness at the interface with the helical elongate element.For some applications, the step of applying the coat of elastomericmaterial to the helical elongate elements as described above, at leastpartially rounds the helical elongate elements.

For some applications, subsequent to the spray having been applied, theassembly of coated helical elongate elements 52, spring 54, andoverexpansion-prevention element 72 is dipped in the elastomer fromwhich film 56 is made. For some applications, the material from whichthe film is made is an elastomer having an ultimate elongation of morethan 300 percent, e.g., more than 400 percent. Typically, the materialhas a relatively low molecular weight. For some applications, thematerial has a melt flow index (which is an indirect measure ofmolecular weight) of at least 4, e.g., at least 4.3. For someapplications, the material has an ultimate tensile strength of more than6000 psi, e.g., more than 7000 psi, or more than 7500 psi. For someapplications, the material is a polycarbonate-based thermoplasticpolyurethane, e.g., a Carbothane™. For some applications, AromaticCarbothane™ (e.g., Aromatic Carbothane™ 75A) is used. Typically, suchmaterials combine one or more of the following properties: no outerdiameter loss caused during the dip process, resistance to fatigue,resistance to becoming misshaped by being crimped, and low outerdiameter loss during crimping. Subsequently, the material is cured suchthat it solidifies, e.g., by being left to dry. Typically, during thisstage, the impeller is disposed on a mandrel, such that the mandrelpasses through lumen 62 defined by the bushings and the spring, therebymaintaining the lumen during the drying. For some applications, whilethe material from which the film is made is drying, the impeller isrotated, which typically facilitates the formation of a film of materialhaving a substantially uniform thickness within each of the impellerblades. Once the material has dried, the mandrel is typically removedfrom lumen 62.

In accordance with the above description of the application of film 56to the helical elongate elements, the scope of the present inventionincludes any technique whereby, prior to the helical elongate elementsbeing dipped into the elastomeric material from which film 56 is made,additional layers of the same elastomeric material, a differentelastomeric material, and/or a mediating material are applied to thehelical elongate elements, whether by spraying, dipping, or a differentcoating method. For some applications, additional layers of elastomericmaterial are configured to round the helical elongate elements, and/orto act as mediators to enhance bonding between the helical elongateelements and film 56 of material. For some applications, a mediatingmaterial (such as silane) is configured to act as a mediator to enhancebonding between the helical elongate elements and film 56 of material.

Typically, impeller 50 is inserted into the left ventricletranscatheterally, while impeller 50 is in a radially-constrainedconfiguration. In the radially-constrained configuration, both helicalelongate elements 52 and central axial spring 54 become axiallyelongated, and radially constrained. Typically film 56 of the material(e.g., silicone and/or polyurethane) changes shape to conform to theshape changes of the helical elongate elements and the axial supportspring, both of which support the film of material. Typically, using aspring to support the inner edge of the film allows the film to changeshape without the film becoming broken or collapsing, due to the springproviding a large surface area to which the inner edge of the filmbonds. For some applications, using a spring to support the inner edgeof the film reduces a diameter to which the impeller can be radiallyconstrained, relative to if, for example, a rigid shaft were to be usedto support the inner edge of the film, since the diameter of the springitself can be reduced by axially elongating the spring.

As described hereinabove, for some applications, proximal bushing 64 ofimpeller 50 is coupled to axial shaft 92 such that the axial position ofthe proximal bushing with respect to the shaft is fixed, and distalbushing 58 of the impeller is slidable with respect to the shaft. Forexample, the proximal bushing may be coupled to coupling element 65disposed on the axial shaft (shown in FIG. 4 ), for example via asnap-fit mechanism. For some applications, when the impeller is radiallyconstrained for the purpose of inserting the impeller into the ventricleor for the purpose of withdrawing the impeller from the subject's body,the impeller axially elongates by the distal bushing sliding along theaxial shaft distally. Alternatively (not shown), distal bushing 58 ofthe impeller is coupled to the shaft such that the axial position of thedistal bushing with respect to the shaft is fixed, and proximal bushing64 of the impeller is slidable with respect to the shaft. For some suchapplications, when the impeller is radially constrained for the purposeof inserting the impeller into the ventricle or for the purpose ofwithdrawing the impeller from the subject's body, the impeller axiallyelongates by the proximal bushing sliding along the axial shaftproximally. Subsequent to being released inside the subject's body, theimpeller assumes its non-radially-constrained configuration (in whichthe impeller is typically disposed during operation of the impeller),which is as shown in FIGS. 3A-E.

Reference is now made to FIGS. 5A and 5B, which are schematicillustrations of impeller 50 and frame 34 of ventricular assist device20, respectively in non-radially-constrained and radially-constrainedstates thereof, in accordance with some applications of the presentinvention. The impeller and the frame are typically disposed in theradially-constrained states during the transcatheteral insertion of theimpeller and the frame into the subject's body, and are disposed in thenon-radially-constrained states during operation of the impeller insidethe subject's left ventricle.

As indicated in FIG. 5B, the frame and the impeller are typicallymaintained in radially-constrained configurations by delivery catheter143. Typically, in the radially-constrained configuration of theimpeller, the impeller has a total length of more than 15 mm (e.g., morethan 20 mm), and/or less than 30 mm (e.g., less than 25 mm), e.g., 15-30mm, or 20-25 mm. Further typically, in the non-radially constrainedconfiguration of the impeller, the impeller has a length of more than 8mm (e.g., more than 10 mm), and/or less than 18 mm (e.g., less than 15mm), e.g., 8-18 mm, or 10-15 mm. Still further typically, when theimpeller and frame 34 are disposed in radially-constrainedconfigurations (as shown in FIG. 5B), the impeller has an outer diameterof less than 2 mm (e.g., less than 1.6 mm) and the frame has an outerdiameter of less than 2.5 mm (e.g., less than 2.1 mm).

As described hereinabove, typically, axial shaft 92 passes through theaxis of impeller 50, via lumen 62 of the impeller. Typically, proximalbushing 64 of the impeller is coupled to the shaft via a couplingelement 65 such that the axial position of the proximal bushing withrespect to the shaft is fixed, and distal bushing 58 of the impeller isslidable with respect to the shaft. (Alternatively, distal bushing 58 ofthe impeller is coupled to the shaft such that the axial position of thedistal bushing with respect to the shaft is fixed, and proximal bushing64 of the impeller is slidable with respect to the shaft.) The axialshaft itself is radially stabilized via a proximal radial bearing 116and a distal radial bearing 118. Typically, proximal bearing housing116H is disposed around, and houses, the proximal bearing, and distalbearing housing 118H is disposed around, and houses, the distal bearing.For some such applications, the radial bearings and the bearing housingsare made of respective, different materials from each other. Forexample, the radial bearings may be made of a first material that has arelatively high hardness, such as ceramic (e.g., zirconia), and thebearing housings may be made of a second material that is moldable intoa desired shape, such as a metal or an alloy (e.g., stainless steel,cobalt chromium, and/or nitinol).

For some applications, axial shaft 92 is made of a metal or an alloy,such as stainless steel. For some such applications, the axial shaftcovered with ceramic sleeves 240 (e.g., zirconia sleeves) along regionsof the axial shaft that come into contact with either of the proximaland distal bearings 116, 118 during operation of the ventricular assistdevice. In this manner, the radial interfaces between the axial shaftand the proximal and distal bearings is a ceramic-ceramic interface. Asdescribed in further detail herein, typically, the impeller and theaxial shaft are configured to undergo axial back-and-forth motion duringoperation of the ventricular assist device. Therefore, for someapplications, at locations along the axial shaft corresponding to eachof the proximal and distal bearing, the axial shaft is covered with theceramic sleeve along a length of more than 5 mm, e.g., more than 7 mm.In this manner, over the course of the axial back-and-forth motion ofthe axial shaft, the regions of the axial shaft that are in contact withthe radial bearings are covered with the ceramic sleeves.

For some applications, the proximal bearing housing 116H and distalbearing housing 118H perform additional functions. Referring first tothe proximal bearing housing, as described hereinabove, for someapplications, proximal strut junctions 33 of frame 34 are closed aroundthe outside of the proximal bearing housing. For some applications, theouter surface of the proximal bearing housing defines groves that areshaped such as to receive the proximal strut junctions. For example, asshown, the proximal strut junctions have widened heads, and the outersurface of the proximal bearing housing defines groves that are shapedto conform with the widened heads of the proximal strut junctions.Typically, securing element 117 (which typically includes a ring) holdsthe strut junctions in their closed configurations around the outside ofproximal bearing housing 116H. For some applications, additionalportions of the ventricular assist device are coupled to the proximalbearing housing. For some applications, a drive cable 130 extends fromoutside the subject's body to axial shaft 92, and is coupled to theaxial shaft. Typically the drive cable rotates within a first outer tube140, which functions as a drive-cable bearing tube, and which extendsfrom outside the subject's body to the proximal bearing housing. Forsome applications, the first outer tube is disposed within a secondouter tube 142, which also extends from outside the subject's body tothe proximal bearing housing. For some applications, first outer tube140 and/or second outer tube 142 is coupled to the proximal bearinghousing (e.g., using an adhesive). For example, first outer tube 140 maybe coupled to an inner surface of the proximal bearing housing, andsecond outer tube 142 may be coupled to an outer surface of the proximalbearing housing.

Referring now to distal bearing housing 118H, for some applications,distal coupling portion 31 of frame 34 is coupled to an outer surface ofdistal bearing housing 118H, e.g., via a snap-fit mechanism. Forexample, the outer surface of a proximal-most portion 119 of the distalbearing housing may include a snap-fit mechanism to which distalcoupling portion 31 of frame 34 is coupled. For some applications,distal bearing 118 is disposed within the proximal-most portion 119 ofthe distal bearing housing, as shown in FIG. 5A. As describedhereinabove, for some applications, pump-outlet tube 24 extends to thedistal end of frame 34 and defines lateral blood-inlet openings 108. Forsome such applications, a coupling portion 41 (e.g., a tubular couplingportion) extends distally from the pump-outlet tube, and the couplingportion is coupled to the distal bearing housing in order to anchor thedistal end of the pump-outlet tube. For some applications, anintermediate portion 123 of the distal bearing housing defines a ridgedor a threaded outer surface, to which coupling portion 41 of thepump-outlet tube is coupled (e.g., via adhesive). For some applications,the outer surface is ridged in order to enhance bonding between thedistal bearing housing and coupling portion 41 of the pump-outlet tube.For some applications, the outer surface is threaded in order to enhancebonding between the distal bearing housing and coupling portion 41 ofthe pump-outlet tube and to facilitate the application of adhesivebetween the outer surface and coupling portion 41 of the pump-outlettube, as described in further detail hereinbelow with reference to FIG.12B. For some applications, a distal portion 121 of the distal bearinghousing is configured to stiffen a region of distal-tip element 107 intowhich the distal end of shaft 92 moves (e.g., axial-shaft-receiving tube126, or a portion thereof). Typically, distal-tip element 107 is coupledto an outer surface of distal portion 121 of the distal bearing housing(e.g., via adhesive). For some applications, at least a portion of theouter surface of distal portion 121 of the distal bearing housing isridged and/or threaded in order to enhance bonding between distal-tipelement 107 and the distal bearing housing.

As described above, axial shaft 92 is radially stabilized via proximalradial bearing 116 and distal radial bearing 118. In turn, the axialshaft, by passing through lumen 62 defined by the impeller, radiallystabilizes the impeller with respect to the inner surface of frame 34and inner lining 39, such that even a relatively small gap between theouter edge of the blade of the impeller and inner lining 39 (e.g., a gapthat is as described above) is maintained, during rotation of theimpeller, as described hereinabove. Typically, the impeller itself isnot directly disposed within any radial bearings or thrust bearings.Rather, bearings 116 and 118 act as radial bearings with respect to theaxial shaft. Typically, pump-head portion 27 (and more generallyventricular assist device 20) does not include any thrust bearing thatis configured to be disposed within the subject's body and that isconfigured to oppose thrust generated by the rotation of the impeller.For some applications, one or more thrust bearings are disposed outsidethe subject's body (e.g., within motor unit 23, shown in FIGS. 1A, 7,and 8A-B), and opposition to thrust generated by the rotation of theimpeller is provided solely by the one or more thrust bearings disposedoutside the subject's body. For some applications, a mechanical elementand/or a magnetic element is configured to maintain the impeller withina given range of axial positions. For example, a magnet (e.g., magnet82, described hereinbelow with reference to FIG. 7 ) that is disposed atthe proximal end of the drive cable (e.g., outside the subject's body)may be configured to impart axial motion to the impeller, and/or tomaintain the impeller within a given range of axial positions.

Reference is now made to FIGS. 6A and 6B, which are schematicillustrations of ventricular assist device 20 at respective stages of amotion cycle of impeller 50 of the ventricular assist device withrespect to frame 34 of the ventricular assist device, in accordance withsome applications of the present invention. For some applications, whilethe impeller is pumping blood through tube 24 by rotating, axial shaft92 (to which the impeller is fixated) is driven to move the impelleraxially back-and-forth within frame 34, by the axial shaft moving in anaxial back-and-forth motion, as described in further detail hereinbelowwith reference to FIG. 7 . Alternatively or additionally, the impellerand the axial shaft are configured to move axially back-and-forth withinframe 34 in response to forces that are acting upon the impeller, andwithout requiring the axial shaft to be actively driven to move in theaxial back-and-forth motion. Typically, over the course of the subject'scardiac cycle, the pressure difference between the left ventricle andthe aorta varies from being approximately zero during ventricularsystole (hereinafter “systole”) to a relatively large pressuredifference (e.g., 50-70 mmHg) during ventricular diastole (hereinafter“diastole”). For some applications, due to the increased pressuredifference that the impeller is pumping against during diastole (and dueto the fact that drive cable 130 is stretchable), the impeller is pusheddistally with respect to frame 34 during diastole, relative to thelocation of the impeller with respect to frame 34 during systole. Inturn, since the impeller is connected to the axial shaft, the axialshaft is moved forward. During systole, the impeller (and, in turn, theaxial shaft) move back to their systolic positions. In this manner, theaxial back-and-forth motion of the impeller and the axial shaft isgenerated in a passive manner, i.e., without requiring active driving ofthe axial shaft and the impeller, in order to cause them to undergo thismotion. FIGS. 6A and 6B show the impeller and axial shaft disposed atrespective positions within frame 34 during the above-described axialback-and-forth motion cycle.

For some applications, by moving in the axial back-and-forth motion, theportions of the axial shaft that are in contact with proximal bearing116 and distal bearing 118 are constantly changing. For some suchapplications, in this manner, the frictional force that is exerted uponthe axial shaft by the bearings is spread over a larger area of theaxial shaft than if the axial shaft were not to move relative to thebearings, thereby reducing wear upon the axial shaft, ceteris paribus.Alternatively or additionally, by moving in the back-and-forth motionwith respect to the bearing, the axial shaft cleans the interfacebetween the axial shaft and the bearings from any residues, such asblood residues.

For some applications, at the proximal-most position of the impellerduring its motion cycle, the proximal end of the impeller within theproximal conical section of frame 34. For some applications, at thedistal-most position of the impeller during its motion cycle, the distalend of the impeller is disposed at the distal end of the cylindricalsection of frame 34. Alternatively, even at the distal-most position ofthe impeller during its motion cycle, the distal end of the impeller isdisposed proximal to the distal end of the cylindrical section of frame34. Typically, over the course of the entire cardiac cycle, the sectionof the impeller at which the span of the impeller is at its maximum isdisposed within the cylindrical portion of the frame 34. However, aproximal portion of the impeller is typically disposed within theproximal conical section of the frame during at least a portion of thecardiac cycle.

Reference is again made to FIGS. 6A and 6B. Typically, distal-tipelement 107 is a single integrated element that includes bothaxial-shaft-receiving tube 126 and distal-tip portion 120. Typically,the axial-shaft receiving tube is configured to receive a distal portionof axial shaft 92 of the pump-head portion during axial back-and-forthmotion of the axial shaft (as described in further detail hereinbelow),and/or during delivery of the ventricular assist device. (Typically,during delivery of the ventricular assist device, the frame ismaintained in a radially-constrained configuration, which typicallycauses the axial shaft to be disposed in a different position withrespect to the frame relative to its disposition with respect to theframe during operation of the ventricular assist device). For someapplications, distal-tip portion 120 is configured to be soft, such thatthe distal-tip portion is configured not to injure tissue of thesubject, even if the distal-tip portion comes into contact with thetissue (e.g., tissue of the left ventricle). For example, distal-tipportion 120 or the entire distal-tip element may be made of silicone,polyethylene terephthalate (PET) and/or polyether block amide (e.g.,PEBAX®). For some applications, the distal-tip portion defines a lumen122 therethrough. For some such applications, during insertion of theventricular assist device into the left ventricle, guidewire 10 (FIG.1B) is first inserted into the left ventricle, for example, inaccordance with known techniques. The distal-tip portion of theventricular assist device is then guided to the left ventricle byadvancing the distal-tip portion over the guidewire, with the guidewiredisposed inside lumen 122. For some applications, a duckbill valve 390(or a different type of hemostasis valve) is disposed at the distal endof lumen 122 of distal-tip portion 120.

Typically, during the insertion of the ventricular assist device intothe subject's ventricle, delivery catheter 143 is placed over impeller50 and frame 34 and maintains the impeller and the frame in theirradially-constrained configurations. For some applications, distal-tipelement 107 extends distally from the delivery catheter during theinsertion of the delivery catheter into the subject's ventricle, asshown in FIG. 1B. For some applications, toward the proximal end of thedistal-tip element, the distal-tip element has a protrusion 110.Referring to FIG. 5B (which shows the pump-head portion disposed insidedelivery catheter 143), for some applications, during the insertion ofthe ventricular assist device into the subject's ventricle, the deliverycatheter extends until the proximal side of the protrusion, such thatthe delivery catheter and the protrusion form a smooth continuoussurface. The distal side of protrusion 110 is tapered, such that thevasculature is exposed to a tapered diameter change, and is not exposedto any edges arising from a sharp change in diameter at the interfacebetween the delivery catheter and the distal-tip element.

For some applications, distal-tip element 107 defines an overallcurvature that is similar to that of a question mark or a tennis-racket,with the distal-tip element defining a straight proximal portion and abulge on one side of the longitudinal axis of the straight proximalportion. Typically, the ventricular assist device is introduced into thesubject's ventricle over a guidewire, as described hereinabove.Distal-tip portion 120 defines lumen 122, such that the distal-tipportion is held in a straightened configuration during the introductionof the ventricular assist device into the subject's ventricle (e.g., asshown in the left frame of FIG. 1B). For some applications, upon theguidewire being removed, distal-tip portion is configured to assume itscurved shape. It is noted that the external shape of distal-tip portionin FIGS. 6A-B (as well as in some other figures) is shown as defining acomplete loop, with the distal end of the distal-tip portion (withinwhich duckbill valve 390 is disposed) crossing over a more proximalportion of the distal-tip portion. Typically, as a result of having hada guidewire inserted therethrough (during insertion of the ventricularassist device into the left ventricle), the distal-tip portion remainspartially straightened, even after the removal of the guidewire from thedistal-tip portion. Typically, the partial straightening of thedistal-tip portion is such that, when the distal-tip portion is disposedwithin the left ventricle, in the absence of external forces acting uponthe distal-tip portion, the distal-tip portion does not define acomplete loop.

Referring again to FIGS. 6A-B, for some applications,axial-shaft-receiving tube 126 extends proximally from distal-tipportion 120 of distal-tip element 107. As described hereinabove,typically, the axial shaft undergoes axial back-and-forth motion duringthe operation of impeller 50. Axial-shaft-receiving tube 126 defineslumen 127, which is configured to receive the axial shaft when the axialshaft extends beyond distal bearing 118. For some applications, theaxial shaft-receiving tube defines a stopper 128 at its distal end, thestopper being configured to prevent advancement of the axial shaftbeyond the stopper. For some applications, the stopper comprises a rigidcomponent that is inserted (e.g., embedded) into the distal end of theshaft-receiving tube. Alternatively (not shown), the stopper comprises ashoulder between lumen 127 of the axial-shaft-receiving tube and lumen122 of distal-tip portion 120.

Typically, during normal operation of the impeller, the axial shaft doesnot come into contact with stopper 128, even when drive cable 130 (shownin FIG. 5A) is maximally elongated (e.g., during diastole). However,stopper 128 is configured to prevent the axial shaft from protrudinginto the tip portion when the delivery catheter is advanced overimpeller 50 and frame 34, during retraction of ventricular assist device20 from the subject's ventricle. In some cases, during the advancementof the delivery catheter over the frame and the impeller, the drivecable is at risk of snapping. In the absence of stopper 128, in suchcases, the axial shaft may protrude into the tip portion. Stopper 128prevents this from happening, even in the event that the drive cablesnaps.

It is noted that, at the proximal end of frame 34, proximal radialbearing 116 also functions as a stopper, by preventing coupling element65 and thereby preventing proximal bushing 64 of impeller 50 from beingable to move beyond the proximal radial bearing. Typically, duringnormal operation of the impeller, coupling element 65 does not come intocontact with proximal radial bearing 116. However, proximal radialbearing 116 is configured to prevent coupling element 65 and therebyprevent proximal bushing 64 of impeller 50 from migrating proximallyfrom inside the frame, for example, when the impeller and the frame areheld in radially-constrained (i.e., crimped) configurations insidedelivery catheter 143.

Typically, during operation of the ventricular assist device, andthroughout the axial back-and-forth motion cycle of the impeller, theimpeller is disposed in relatively close proximity to the distal-tipportion. For example, the distance of the impeller to the distal-tipportion may be within the distal-most 50 percent, e.g., the distal-most30 percent (or the distal-most 20 percent) of tube 24, throughout theaxial back-and-forth motion cycle of the impeller.

Reference is now made to FIG. 7 , which is a schematic illustration ofan exploded view of motor unit 23 of ventricular assist device 20, inaccordance with some applications of the present invention. For someapplications, computer processor 25 of control console 21 (FIG. 1A) thatcontrols the rotation of impeller 50 is also configured to control theback-and-forth motion of the axial shaft. Typically, both types ofmotion are generated using motor unit 23. The scope of the presentinvention includes controlling the back-and-forth motion at anyfrequency. For some applications, an indication of the subject's cardiaccycle is detected (e.g., by detecting the subject's ECG), and theback-and-forth motion of the axial shaft is synchronized to thesubject's cardiac cycle.

Typically, motor unit 23 includes a motor 74 that is configured toimpart rotational motion to impeller 50, via drive cable 130. Asdescribed in further detail hereinbelow, typically, the motor ismagnetically coupled to the drive cable. For some applications, an axialmotion driver 76 is configured to drive the motor to move in an axialback-and-forth motion, as indicated by double-headed arrow 79.Typically, by virtue of the magnetic coupling of the motor to the drivecable, the motor imparts the back-and-forth motion to the drive cable,which it turn imparts this motion to the impeller. As describedhereinabove and hereinbelow, for some applications, the drive cable, theimpeller, and/or the axial shaft undergo axial back-and-forth motion ina passive manner, e.g., due to cyclical changes in the pressure gradientagainst which the impeller is pumping blood. Typically, for suchapplications, motor unit 23 does not include axial motion driver 76.

For some applications, the magnetic coupling of the motor to the drivecable is as shown in FIG. 7 . As shown in FIG. 7 , a set of drivingmagnets 77 are coupled to the motor via a driving magnet housing 78. Forsome applications, the driving magnet housing includes ring 81 (e.g., asteel ring), and the driving magnets are adhered to an inner surface ofthe ring. For some applications a spacer 85 is adhered to the innersurface of ring 81, between the two driving magnets, as shown. A drivenmagnet 82 is disposed between the driving magnets such that there isaxial overlap between the driving magnets and the driven magnet. Thedriven magnet is coupled to a pin 131, which extends to beyond thedistal end of driven magnet 82, where the pin is coupled to the proximalend of drive cable 130. For example, the driven magnet may becylindrical and define a hole therethrough, and pin 131 may be adheredto an inner surface of the driven magnet that defines the hole. For someapplications, the driven magnet is cylindrical, and the magnet includesa North pole and a South pole, which are divided from each other alongthe length of the cylinder along a line 83 that bisects the cylinder, asshown. For some applications, the driven magnet is housed inside acylindrical housing 87. Typically, pin 131 defines a guidewire lumen133.

It is noted that in the application shown in FIG. 7 , the drivingmagnets are disposed outside the driven magnet. However, the scope ofthe present application includes reversing the configurations of thedriving magnets and the driven magnet, mutatis mutandis. For example,the proximal end of the drive cable may be coupled to two or more drivenmagnets, which are disposed around a driving magnet, such that there isaxial overlap between the driven magnets and the driving magnet.

As described hereinabove, typically purging system 29 (shown in FIG. 1A)is used with ventricular assist device 20. Typically, motor unit 23includes an inlet port 86 and an outlet port 88, for use with thepurging system. For some applications, a purging fluid is continuouslyor periodically pumped into the ventricular assist device via inlet port86 and out of the ventricular assist device via outlet port 88.

Typically, magnet 82 and pin 131 are held in axially fixed positionswithin motor unit 23. The proximal end of the drive cable is typicallycoupled to pin 131 and is thereby held in an axially fixed position bythe pin. Typically, drive cable 130 extends from pin 131 to axial shaft92 and thereby at least partially fixes the axial position of the axialshaft, and in turn impeller 50. For some applications, the drive cableis somewhat stretchable. For example, the drive cable may be made ofcoiled wires that are stretchable. The drive cable typically allows theaxial shaft (and in turn the impeller) to assume a range of axialpositions (by the drive cable becoming more or less stretched), butlimits the axial motion of the axial shaft and the impeller to beingwithin a certain range of motion (by virtue of the proximal end of thedrive cable being held in an axially fixed position, and thestretchability of the drive cable being limited).

As described hereinabove, for some applications, impeller 50 and axialshaft 92 are configured to move axially back-and-forth within frame 34in response to forces that act upon the impeller, and without requiringthe axial shaft to be actively driven to move in the axialback-and-forth motion. Typically, over the course of the subject'scardiac cycle, the pressure difference between the left ventricle andthe aorta varies from being approximately zero during systole to arelatively large pressure difference (e.g., 50-70 mmHg) during diastole.For some applications, due to the increased pressure difference that theimpeller is pumping against during diastole (and due to the drive cablebeing stretchable), the impeller is pushed distally with respect toframe 34 during diastole, relative to the location of the impeller withrespect to frame 34 during systole. In turn, since the impeller isconnected to the axial shaft, the axial shaft is moved forward. Duringsystole, the impeller (and, in turn, the axial shaft) move back to theirsystolic positions. In this manner, the axial back-and-forth motion ofthe impeller and the axial shaft is generated in a passive manner, i.e.,without requiring active driving of the axial shaft and the impeller, inorder to cause them to undergo this motion.

Reference is now made to FIGS. 8A and 8B, which are schematicillustrations of motor unit 23, in accordance with some applications ofthe present invention. In general, motor unit 23 as shown in FIGS. 8Aand 8B is similar to that shown in FIG. 7 , and, unless describedotherwise, motor unit 23 as shown in FIGS. 8A and 8B contains similarcomponents to motor unit 23 as shown in FIG. 7 . For some applications,the motor unit includes a heat sink 90 that is configured to dissipateheat that is generated by the motor. Alternatively or additionally, themotor unit includes ventilation ports 93 that are configured tofacilitate the dissipation of heat that is generated by the motor. Forsome applications, the motor unit includes vibration dampeners 94 and 96that are configured to dampen vibration of the motor unit that is causedby rotational motion and/or axial back-and-forth motion of components ofthe ventricular assist device.

Reference is now made to FIGS. 9A and 9B, which are schematicillustrations of ventricular assist device 20, the device includinginner lining 39 that lines the inside of frame 34 that houses impeller50, in accordance with some applications of the present invention. Forsome applications, inner lining 39 is disposed inside frame 34, in orderto provide a smooth inner surface (e.g., a smooth inner surface having asubstantially circular cross-sectional shape) through which blood ispumped by impeller. Typically, by providing a smooth surface, thecovering material reduces hemolysis that is caused by the pumping ofblood by the impeller, relative to if the blood were pumped between theimpeller and struts of frame 34. For some applications, inner liningincludes polyurethane, polyester, and/or silicone. Alternatively oradditionally, the inner lining includes polyethylene terephthalate (PET)and/or polyether block amide (PEBAX®).

Typically, the inner lining is disposed over the inner surface of atleast a portion of central cylindrical portion 38 of frame 34. For someapplications, pump-outlet tube 24 also covers central cylindricalportion 38 of frame 34 around the outside of the frame, for example,such that pump-outlet tube 24 and inner lining 39 overlap over at least50 percent of the length of the inner lining, for example, over theentire length of the cylindrical portion of frame 34, e.g., as shown inFIG. 9A. For some applications, there is only partial overlap betweenpump-outlet tube 24 and inner lining 39, e.g., as shown in FIG. 9B. Forexample, pump-outlet tube 24 may overlap with inner lining along lessthan 50 percent (e.g., along less than 25 percent) of the length of theinner lining. For some such applications, during insertion ofventricular assist device 20 into the subject's body, the impeller isadvanced distally within frame 34, such that the impeller is notdisposed within the area of overlap between the pump-outlet tube and theinner lining, such that there is no longitudinal location at which theimpeller, pump-outlet tube 24, frame 34, and inner lining 39 all overlapwith each other. As shown in FIGS. 9A and 9B, for some applications asingle axially-facing blood inlet opening 108 is defined at the distalend of the pump-outlet tube and/or the inner lining. Alternatively, theinner lining is disposed over the inner surface of at least a portion ofcentral cylindrical portion 38 of frame 34, and the pump-outlet tubeextends to the distal end of the frame and defines a plurality oflateral blood-inlet openings 108. Such applications are described infurther detail hereinbelow with reference to FIGS. 11A-13B, for example.

Typically, over the area of overlap between inner lining 39 andpump-outlet tube 24, the inner lining is shaped to form a smooth surface(e.g., in order to reduce hemolysis, as described hereinabove), andpump-outlet tube 24 is shaped to conform with the struts of frame 34(e.g., as shown in the cross-section in FIG. 9A). Further typically, theinner lining has a substantially circular cross-section (for example,due to the relatively small cell width within the central cylindricalportion of the frame, as described hereinabove, with reference to FIG. 2). For some applications, over the area of overlap between inner lining39 and pump-outlet tube 24, the pump-outlet tube and the inner liningare coupled to each other, e.g., via vacuum, via an adhesive, and/orusing a thermoforming procedure, for example as described hereinbelow.

For some applications, inner lining 39 and pump-outlet tube 24 are madeof different materials from each other. For example, the inner liningmay be made of polyurethane, and the pump-outlet tube may be made ofpolyether block amide (PEBAX®). Typically, for such applications, thematerial from which the inner lining is made has a higher thermoformingtemperature than that of the material from which the pump-outlet tube ismade. Alternatively, inner lining 39 and pump-outlet tube 24 are made ofthe same material as each other. For example, the both the inner liningand the pump-outlet tube may be made of may be made of polyurethane orpolyether block amide (PEBAX®).

For some applications, the pump-outlet tube and the inner lining arebonded to each other and/or the frame in the following manner. For someapplications, the inner lining is directly bonded to the inner surfaceof the frame, before the pump-outlet tube is bonded to the outside ofthe frame. It is noted that, by bonding the inner lining directly to theinner surface of the frame, (rather than simply bonding the inner liningto the pump-outlet tube and thereby sandwiching the frame between theinner lining to the pump-outlet tube), any air bubbles, folds, and otherdiscontinuities in the smoothness of the surface provided by the innerlining are typically avoided. For some applications, similar techniquesto those described hereinabove, for enhancing bonding between theelastomeric film and the helical elongate elements of the impeller, areused to enhance bonding between the inner lining and the inner surfaceof the frame. For some applications, initially, the frame is treated soas to enhance bonding between the inner lining and the inner surface ofthe frame. For some applications, the treatment of the frame includesapplying a plasma treatment to the frame (e.g., to the inner surface ofthe frame), dipping the frame in a coupling agent that has at least twofunctional groups that are configured to bond respectively with theframe and with the material form which the inner lining is made (e.g.,silane solution), and/or dipping the frame in a solution that containsthe material from which the inner lining is made (e.g., polyurethanesolution). For some applications, the inner lining is made of anelastomeric material (e.g., polyurethane) and the coupling agent is asilane solution, such as a solution ofn-(2-aminoethyl)-3-aminopropyltrimethoxysilane, with the silanecontaining a first functional group (e.g., (OH)) which is configured tobond with the frame (which is typically made of an alloy, such anitinol), and the silane containing a second functional group (e.g.,(NH2)) which is configured to bond with the elastomeric material.

For some applications, subsequently, a solution that contains thematerial from which the inner lining is made (e.g., polyurethanesolution) is sprayed over the central cylindrical portion of the cage.Once the inner surface of the frame has been treated, the inner liningis bonded to the inner surface of the central cylindrical portion of theframe (e.g., to the inner surface of a central cylindrical portion ofthe frame). Typically, the inner lining (which is shaped as a tube), isplaced over a mandrel, the frame is placed over the inner lining, andpressure is applied by a heat shrinking process. Further typically, theassembly of the inner lining and the frame is heated in an oven.

Subsequent to the inner lining having been bonded to the frame, aportion of pump-outlet tube 24 is placed around the outside of theframe. As described above, for some applications, inner lining 39 andpump-outlet tube 24 are made of different materials from each other. Forexample, the inner lining may be made of polyurethane, and thepump-outlet tube may be made of polyether block amide (PEBAX®).Typically, for such applications, the material from which the innerlining is made has a higher thermoforming temperature than that of thematerial from which the pump-outlet tube is made. For some applications,in order to mold pump-outlet tube 24 to conform with the struts of frame34, without causing the inner lining to deform, the frame is heated to atemperature that is above the thermoforming temperature of pump-outlettube 24 but below the thermoforming temperature of inner lining 39.

Typically, the frame is heated from inside the frame, using the mandrel.Typically, while the frame is heated to the aforementioned temperature,an outer tube (which is typically made from silicone) applies pressureto pump-outlet tube 24 that causes pump-outlet tube 24 to be pushedradially inwardly, in order to cause the pump-outlet tube to conformwith the shapes of the struts of the frame, as shown in thecross-section of FIG. 9A. For some applications, during this stage, themandrel that is placed inside the inner lining and which heats the innerlining is shorter than the length of the inner lining. The mandrel istypically placed within the inner lining such that margins are leftoutside of the mandrel at each of the ends of the inner lining.Typically, the inner lining acts as a shield to protect the pump-outlettube from being overheated and becoming damaged by the heating of themandrel. Placing the inner lining on the mandrel in the aforementionedmanner prevents the mandrel from coming into direct contact with theframe and/or the pump-outlet tube. For some applications, thecombination of the frame, the inner lining, and the portion ofpump-outlet tube 24 disposed around the frame is subsequently shape setto a desired shape and dimensions using shape setting techniques thatare known in the art.

Reference is now made to FIGS. 10A, 10B and 10C, which are schematicillustrations of a portion of a ventricular assist device 20, theventricular assist device including a protective braid 150 at a distalend thereof, in accordance with some applications of the presentinvention. For some applications, pump-outlet tube 24 and inner lining39 extend until the end of the cylindrical portion 38 of frame 34, asshown in FIGS. 10A-C. For some applications, in order to reduce a riskof structures from the left ventricle (such as chordae tendineae,trabeculae carneae, and/or papillary muscles) entering into frame 34 andpotentially being damaged by the impeller and/or the axial shaft, and/orcausing damage to the left ventricular assist device, distal conicalportion 40 of the frame is covered (internally or externally) withprotective braid 150. Typically, within at least a portion of thecylindrical portion of the frame, the braid is embedded between thepump-outlet tube and the inner lining, such that, during crimping of theframe, the braid becomes crimped with the pump-outlet tube and the innerlining, thereby preventing the braid from moving with respect topump-outlet tube and/or the inner lining (The region in which theprotective braid is embedded between the pump-outlet tube and the innerlining is not visible in FIGS. 10A-C, as it is covered by thepump-outlet tube.)

For some applications, protective braid 150 extends substantially untilthe distal end of the distal conical portion of the frame, as shown inFIG. 10A. For some such applications, along a distal part 152 of thedistal conical portion of the frame, the braid is covered with ablood-impermeable material 154 (e.g., polyurethane, polyester, silicone,polyethylene terephthalate (PET) and/or polyether block amide (e.g.,PEBAX®)), as shown in FIG. 10A. Typically, most of the blood flow intoblood-inlet opening 108 defined by the pump-outlet tube is from thesides of the distal conical portion of the frame, and there isrelatively little axial flow via the distal end of the distal conicalportion of the frame. Therefore, in some cases, there is a risk ofstagnation in this region. In addition, the holes defined by the braidare typically smaller within distal part 152 of the distal conicalportion of the frame, due to the narrowing of the frame. Both of thesefactors can lead to thrombi forming on the braid within the distal part152 of the distal conical portion of the frame. Therefore, for someapplications, the braid is covered along distal part 152 of the distalconical portion of the frame, in order to prevent thrombi from formingon the braid within this part. Typically, the braid is covered (forexample, with a blood-impermeable elastomeric material, such aspolyurethane). Alternatively, the pattern of the braid does not extendto the distal end of the distal conical portion of the frame. Rather,within distal part 152 of the distal conical portion of the frame thebraid is opened or cut, such as to define large apertures 156, as shownin FIG. 10B.

For some applications (not shown), within distal part 152 of the distalconical portion of the frame, the braid is covered (for example, with ablood-impermeable elastomeric material, such as polyurethane), andlarger apertures are then cut from the covered braid. Alternatively oradditionally (also not shown), within distal part 152 of the distalconical portion of the frame, the braid is covered with ablood-impermeable elastomeric material, e.g., polyurethane, and anaperture is then cut from the covered braid around the fullcircumference of the frame, such that that the covered braid defines anaperture that extends around the full circumference of distal part 152of the distal conical portion of the frame. For some such applications,the above-described aperture is cut such that it extends until thedistal end of the distal conical portion of the frame, i.e., such thatthere is a single aperture that extends around the full circumference ofthe frame and until the distal end of the distal conical portion of theframe.

For some applications, the braid extends substantially until the distalend of the distal conical portion of the frame, and the braid is notcovered even within distal part 152 of the distal conical portion of theframe, as shown in FIG. 10C. For some applications, the braid is woveninto struts of the distal conical portion of frame 34, as shown in theenlarged frame in FIG. 10C.

Reference is now made to FIGS. 11A-D, which are schematic illustrationsof pump-outlet tube 24 or a portion thereof, the pump-outlet tube beingconfigured to define lateral blood-inlet openings 108 at a distal endthereof, in accordance with some applications of the present invention.For some applications, the pump-outlet tube extends substantially untilthe distal end of distal conical portion 40 of frame 34. For suchapplications, the pump-outlet tube typically defines a distal conicalportion 46 which is distally facing, i.e., facing such that the narrowend of the cone is distal with respect to the wide end of the cone.Typically, the pump-outlet tube includes coupling portion 41 (e.g., atubular coupling portion, as shown), which extends distally from thepump-outlet tube. As described hereinabove, the coupling portion iscoupled to the distal bearing housing in order to anchor the distal endof the pump-outlet tube.

For some applications (not shown), the pump-outlet tube defines two tofour lateral blood-inlet openings. Typically, for such applications,each of the blood-inlet openings defines an area of more than 20 squaremm (e.g., more than 30 square mm), and/or less than 60 square mm (e.g.,less than 50 square mm), e.g., 20-60 square mm, or 30-50 square mm.Alternatively or additionally, the outlet tube defines a greater numberof smaller blood-inlet openings 108, e.g., more than 10 blood-inletopenings, more than 50 blood-inlet openings, more than 100 blood-inletopenings, or more than 150 blood-inlet openings, e.g., 50-100blood-inlet openings, 100-150 blood-inlet openings, or 150-200blood-inlet openings. For some applications, the blood-inlet openingsare sized such as (a) to allow blood to flow from the subject's leftventricle into the tube and (b) to block structures from the subject'sleft ventricle from entering into the frame. Typically, for suchapplications, the distal conical portion 46 of pump-outlet tube 24 isconfigured to reduce a risk of structures from the left ventricle (suchas chordae tendineae, trabeculae carneae, and/or papillary muscles)entering into frame 34 and potentially being damaged by the impellerand/or the axial shaft, and/or causing damage to the left ventricularassist device. Therefore, for some applications, the blood-inletopenings are shaped such that, in at least one direction, the widths (orspans) of the openings are less than 1 mm, e.g., 0.1-1 mm, or 0.3-0.8mm. By defining such a small width (or span), it is typically the casethat structures from the left ventricle (such as chordae tendineae,trabeculae carneae, and/or papillary muscles) are blocked from enteringinto frame 34. For some such applications, each of the blood-inletopenings defines an area of more than 0.05 square mm (e.g., more than0.1 square mm), and/or less than 3 square mm (e.g., less than 1 squaremm), e.g., 0.05-3 square mm, or 0.1-1 square mm. Alternatively, each ofthe blood-inlet openings defines an area of more than 0.1 square mm(e.g., more than 0.3 square mm), and/or less than 5 square mm (e.g.,less than 1 square mm), e.g., 0.1-5 square mm, or 0.3-1 square mm.

Typically, the portion of the pump-outlet tube that defines theblood-inlet openings has a porosity of more than 40 percent, e.g., morethan 50 percent, or more than 60 percent (where porosity is defined asthe percentage of the area of this portion that is porous to bloodflow). Thus, on the one hand, the blood-inlet openings are relativelysmall (in order to prevent structures of the left ventricular fromentering the frame), but on the other hand, the porosity of the portionof the pump-outlet tube that defines the blood-inlet openings isrelatively high, such as to allow sufficient blood flow into thepump-outlet tube.

For some applications, each the blood-inlet openings has a circular or apolygonal shape. For some applications, each of the blood-inlet openingshas a hexagonal shape, as shown in FIGS. 11A-D. Typically, usingopenings having a hexagonal shape allows the portion of the pump-outlettube that defines the blood-inlet openings to have a relatively highporosity (e.g., as described hereinabove), while providing the portionof the pump-outlet tube that defines the blood-inlet openings withsufficient material between the blood-inlet openings to prevent tearingand/or stretching of the material. As shown in FIG. 11B, for someapplications, a width W of gaps between adjacent hexagonal (or otherpolygonal) holes is more than 0.01 mm (e.g., more than 0.04 mm), and/orless than 0.1 mm (e.g., less than 0.08 mm), for example, 0.01-0.1 mm, or0.04-0.08 mm. For some applications, the distance D between opposingsides of each of the hexagons (or other types of polygons) is more than0.2 mm (e.g., more than 0.4 mm) and/or less than 0.8 mm (e.g., less than0.6 mm), e.g., 0.2-0.8 mm, or 0.4-0.6 mm. As indicated in FIG. 11B,typically each of the polygons encloses a circle (such that anystructure that cannot pass through such a circle would be unable to passthrough the polygon). Typically, the diameter of the circle enclosed bythe polygon is the equivalent of distance D, e.g., more than 0.2 mm(e.g., more than 0.4 mm) and/or less than 0.8 mm (e.g., less than 0.6mm), e.g., 0.2-0.8 mm, or 0.4-0.6 mm.

FIG. 11D shows a segment of distal conical portion 46 of pump-outlettube 24, in accordance with some applications of the present invention.In the view shown in FIG. 11D, the segment is laid our flat forillustrative purposes. As shown in FIG. 11D, for some applications,within a proximal region 46P of distal conical portion 46 of pump-outlettube 24, the widths W1 of the gaps between the hexagonal (or other typeof polygonal) holes are larger than widths W of the gaps between thehexagonal (or other type of polygonal) holes within a distal region 46Dof distal conical portion 46 of the pump-outlet tube. For someapplications, the ratio of the widths of gaps between adjacentblood-inlet openings with the proximal region of the distal portion ofthe pump-outlet tube to the widths of gaps between adjacent blood-inletopenings within the distal region of the distal portion of thepump-outlet tube is greater than 3:2, e.g., between 3:2 and 5:2.Typically, for such applications, within proximal region 46P of distalconical portion 46 of pump-outlet tube 24, a distance D1 betweenopposing sides of each of the hexagons (or other type of polygons) issmaller than distance D between opposing sides of each of the hexagons(or other type of polygons) within distal region 46D of distal conicalportion 46 of the pump-outlet tube. (As described hereinabove,typically, distances D and D1 also represent the diameter of a circlethat is enclosed by the respectively sized polygons.) For someapplications, the ratio of the diameter of a circle enclosed by each ofthe blood-inlet openings with the distal region of the distal portion ofthe pump-outlet tube to a diameter of a circle enclosed by each of theblood-inlet openings with the proximal region of the distal portion ofthe pump-outlet tube is greater than 7:6, e.g., between 7:6 and 4:3.Further typically, within distal region 46D, the distal conical portionof pump-outlet tube 24, has a higher porosity than within proximalregion 46P of the distal conical portion 46 of the pump-outlet tube. Forexample, the ratio of the porosity within distal region 46D to theporosity within proximal region 46P is more than 4:3, or more than 3:2.For some applications, the proximal region extends along a length ofmore than 0.5 mm, and/or less than 2 mm (e.g., less than 1.5 mm), forexample, between 0.5-2 mm or 0.5-1.5 mm. For some applications, thetotal length of the distal conical portion is more than 6 mm and/or orless than 12 mm (e.g., less than 10 mm), for example between 6-12 mm, or6-10 mm.

As described hereinabove with reference to FIGS. 9A-B, typically, thepump-outlet tube is coupled to frame 34 via heating. For someapplications, within the proximal region 46P of distal conical portion46 of pump-outlet tube 24, the gaps between the blood-inlet holes arewider and/or the blood-inlet holes are smaller than within distal region46D, and/or the porosity is lower than within distal region 46D, inorder to prevent and/or reduce damage (e.g., tearing, thinning, and/orstretching) that may be caused to the material that defines theblood-inlet holes from being damaged during the above-described heatingprocess.

Typically, width W of the gaps between the hexagonal (or other type ofpolygonal) holes and distance D between opposing sides of each of thehexagons (or other type of polygons) within distal region 46D of distalconical portion 46 of the pump-outlet tube are as described hereinabove.For some applications, width W1 of gaps between adjacent hexagonal (orother polygonal) holes within proximal region 46P of distal conicalportion 46 of pump-outlet tube 24 is more than 0.05 mm (e.g., more than0.07 mm), and/or less than 0.2 mm (e.g., less than 0.15 mm), forexample, 0.05-0.2 mm, or 0.07-0.15 mm. For some applications, distanceD1 between opposing sides of each of the hexagons (or other types ofpolygons) within proximal region 46P of distal conical portion 46 ofpump-outlet tube 24 is more than 0.1 mm (e.g., more than 0.3 mm) and/orless than 0.6 mm (e.g., less than 0.5 mm), e.g., 0.1-0.6 mm, or 0.3-0.5mm.

The scope of the present disclosure includes having non-uniformly sizedand/or shaped lateral blood-inlet openings (e.g., circular, rectangular,polygonal, and/or hexagonal lateral blood-inlet openings), disposed inany arrangement along the distal conical portion 46 of the pump-outlettube. Similarly, the scope of the present disclosure includes a distalconical portion 46 of the pump-outlet tube that defines lateralblood-inlet openings being arranged such that the distal conical portionhas a non-uniform porosity, with the porosity varying over differentregions of the distal conical portion. For some applications, the shapesand/or sizes of the lateral blood-inlet openings, and/or the porosity ofthe distal conical portion, is varied such as to account for varyingblood flow dynamics at different regions of the distal conical portion.Alternatively or additionally, the shapes and/or sizes of the lateralblood-inlet openings, and/or the porosity of the distal conical portion,is varied such as to account for changes in the shape of the distalconical portion along its length.

Reference is now made to FIGS. 12A-B, which are schematic illustrationsof pump-outlet tube 24 or a portion thereof, the pump-outlet tube beingconfigured to define lateral blood-inlet openings 108 at a distal endthereof, in accordance with some applications of the present invention.As described with reference to FIGS. 11A-D, for some applications, thepump-outlet tube extends substantially until the distal end of distalconical portion 40 of frame 34. For such applications, the pump-outlettube typically defines a distal conical portion 46 which is distallyfacing, i.e., facing such that the narrow end of the cone is distal withrespect to the wide end of the cone. For some applications, thepump-outlet tube defines more than 10 blood-inlet openings, more than 50blood-inlet openings, more than 100 blood-inlet openings, or more than150 blood-inlet openings, e.g., 50-100 blood-inlet openings, 100-150blood-inlet openings, or 150-200 blood-inlet openings. For someapplications, the blood-inlet openings are sized such as (a) to allowblood to flow from the subject's left ventricle into the tube and (b) toblock structures from the subject's left ventricle from entering intothe frame. Typically, for such applications, the distal conical portion46 of pump-outlet tube 24 is configured to reduce a risk of structuresfrom the left ventricle (such as chordae tendineae, trabeculae carneae,and/or papillary muscles) entering into frame 34 and potentially beingdamaged by the impeller and/or the axial shaft, and/or causing damage tothe left ventricular assist device. Therefore, for some applications,the blood-inlet openings are shaped such that, in at least onedirection, the widths (or spans) of each of the openings are less than 1mm, e.g., 0.1-1 mm, or 0.3-0.8 mm. By defining such a small width (orspan), it is typically the case that structures from the left ventricle(such as chordae tendineae, trabeculae carneae, and/or papillarymuscles) are blocked from entering into frame 34. For some suchapplications, each of the blood-inlet openings defines an area of morethan 0.05 square mm (e.g., more than 0.1 square mm), and/or less than 3square mm (e.g., less than 1 square mm), e.g., 0.05-3 square mm, or0.1-1 square mm. Alternatively, each of the blood-inlet openings definesan area of more than 0.1 square mm (e.g., more than 0.3 square mm),and/or less than 5 square mm (e.g., less than 1 square mm), e.g., 0.1-5square mm, or 0.3-1 square mm.

For some applications, the blood-inlet openings define generallyrectangular shapes, as shown in FIGS. 12A-B. For some such applications,the ratio of the lengths to the widths of the blood-inlet openings isbetween 1.1:1 and 4:1, e.g., between 3:2 and 5:2. For some applications,by having such shapes, the blood-inlet openings are configured (a) toblock structures from the left ventricle (such as chordae tendineae,trabeculae carneae, and/or papillary muscles) from entering into frame34, but (b) to provide the portion of the pump-outlet tube that definesthe blood-inlet openings with a relatively high porosity. Typically, theportion of the pump-outlet tube that defines the blood-inlet openingshas a porosity of more than 40 percent, e.g., more than 50 percent, ormore than 60 percent (where porosity is defined as the percentage of thearea of this portion that is porous to blood flow). Thus, on the onehand the blood-inlet openings are relatively small (in order to preventstructures of the left ventricular from entering the frame), but on theother hand, the porosity of the portion of the pump-outlet tube thatdefines the blood-inlet openings is relatively high, such as to allowsufficient blood flow into the pump-outlet tube.

Typically, the pump-outlet tube includes a coupling portion 41 (e.g., atubular coupling portion, as shown), which extends distally from thepump-outlet tube. As described hereinabove, the coupling portion iscoupled to distal bearing housing 118H in order to anchor the distal endof the pump-outlet tube. Also as described hereinabove, typically, thepump-outlet tube is coupled to the outside of the central cylindricalportion of the frame. For some applications, distal conical portion 46of the pump-outlet tube is not itself bonded to distal conical portion40 of the frame. Rather, distal conical portion 46 of the pump-outlettube is held in place with respect to distal conical portion 40 of theframe, by virtue of coupling portion 41 being coupled to distal bearinghousing 118H and the pump-outlet tube being coupled to the outside ofthe central cylindrical portion of the frame. Alternatively, the distalconical portion 46 of the pump-outlet tube is directly coupled to distalconical portion 40 of the frame (e.g., via heat shrinking).

As described hereinabove, for some applications, coupling portion 41 iscoupled to the outer surface of portion 123 of distal bearing housing118H. For some applications, coupling portion 41 defines a hole 111(e.g., toward the distal end of the coupling portion), as shown in FIG.12B. For some applications, adhesive is applied between coupling portion41 and the outer surface of portion 123 of distal bearing housing 118H,via the hole. As described hereinabove, for some application, the outersurface of portion 123 of distal bearing housing 118H is threaded.Typically, the threaded outer surface allows the adhesive to graduallyand uniformly spread between coupling portion 41 and the outer surfaceof portion 123 of distal bearing housing 118H. Further typically, thecoupling portion is transparent, such that the spread of the adhesive isvisible through the coupling portion. Therefore, for some applications,once the adhesive has sufficiently spread between coupling portion 41and the outer surface of portion 123 of distal bearing housing 118H(e.g., once the outer surface of portion 123 has been covered with theadhesive), application of the adhesive is terminated.

It is noted that the above description of methods and apparatus forbonding distal conical portion 46 of the pump-outlet tube with respectto other portions of the ventricular assist device is applicable to anyembodiments of the distal conical portions 46 of the pump-outlet tubethat are described herein, including any one of the embodimentsdescribed with reference to FIGS. 11A-13B. For some applications,similar techniques are used to bond protective braid 150 (shown in FIGS.10A-C) to the distal bearing housing.

It is noted that, although the above description of methods andapparatus for bonding a coupling portion to a surface have beendescribed with reference to the distal portion of the pump-outlet tubeand the outer surface of the distal bearing housing, similar apparatusand methods are applicable to any type of inlet guard (i.e., any elementthat is disposed over the distal conical portion of the frame anddefines blood-inlet openings that are sized such as (a) to allow bloodto flow from the subject's left ventricle into the tube and (b) to blockstructures from the subject's left ventricle from entering into theframe) and any surface that is disposed distally to the frame.

Reference is now made to FIGS. 13A-B, which are schematic illustrationsof pump-outlet tube 24 or a portion thereof, the pump-outlet tube beingconfigured to define lateral blood-inlet openings 108 at a distal endthereof, in accordance with some applications of the present invention.Pump-outlet tube 24 of FIGS. 13A-B is generally similar to that shown inFIGS. 12A-B except for the differences described below. As describedwith reference to FIG. 10A, typically, most of the blood flow intoblood-inlet openings 108 is from the sides of the distal conical portionof the frame, and there is relatively little axial flow via the distalend of the distal conical portion of the frame. Therefore, in somecases, there is a risk of stagnation in this region, which can lead tothrombi forming within the distal end of the distal conical portion ofthe frame. Moreover, due to the lower blood flow, there is a lower riskof structures from the left ventricle (such as chordae tendineae,trabeculae carneae, and/or papillary muscles) entering into frame 34 viathis region. Therefore, for some applications, along a distal part 158of distal conical portion 46 of pump-outlet tube 24 (which typicallycovers the distal part of the distal conical portion of the frame), thepump-outlet tube 24 defines large blood-inlet openings 108L, whichreduces the risk of thrombosis relative to if the blood-inlet openingsalong distal part 158 of distal conical portion 46 of pump-outlet tube24 were smaller. (In some cases distal part 158 corresponds to distalregion 46D, shown in FIG. 11D.) Typically, the large blood-inletopenings 108L have trapezoidal or triangular shapes. For someapplications, the shapes of the large blood-inlet openings conforms withthe shapes of the struts of the frame within the distal part of theframe. That is to say that the borders 159 of the large blood-inletopenings lie along struts of the distal portion of the frame, and theopenings themselves lie over the openings defined by the struts. Forsome applications, there are between 4 and 12 (e.g., between 6 and 10)large blood-inlet openings. Typically each of the large blood-inletopenings has an area of 1-7 square mm, e.g., 2-5 square mm, or 3-4square mm. For some applications, a ratio of the area of the smallest oflarge blood-inlet openings 108L to the largest of the smallerblood-inlet openings 108 is more than 3:1, e.g., more than 4:1.Typically, within distal part 158 of distal conical portion 46 ofpump-outlet tube 24, tube 24 has a porosity of more than 55 percent,e.g., more than 65 percent.

Reference is now made to FIGS. 14A and 14B, which are schematicillustrations of frame 34 of ventricular assist device 20, the frameincluding a protective braid 155 at a proximal end thereof, inaccordance with some applications of the present invention. For someapplications, the protective braid is disposed over (or within) theproximal conical section of frame 34. For example, the protective braidmay be woven into struts of the frame in a similar manner to thatdescribed with reference to FIG. 10C. Typically, the protective braid isconfigured to act as a filter, for example by preventing any elementsthat are greater than a given size (e.g., thrombi) from migratingproximally along pump-outlet tube 24. The protective braid is used incombination with any one of the embodiments described herein. Forexample, the protective braid may be used with a pump-outlet tube thatdefines a single axially-facing blood-inlet opening 108 (as shown inFIG. 14A), or it may be used with a pump-outlet tube that defineslateral blood-inlet openings 108 (as shown in FIG. 14B).

Reference is now made to FIG. 15 , which is a schematic illustration ofpump-outlet tube 24 that defines blood-outlet openings 109 at a proximalend thereof, in accordance with some applications of the presentinvention. For some applications, the blood-outlet openings are sizedand shaped in similar shapes and sizes to any one of the embodiments oflateral blood-inlet openings 108 described herein. For someapplications, by having such shapes, the region of the pump-outlet tubethat defines the blood-outlet openings is configured (a) act as afilter, for example, by preventing any elements that are greater than agiven size (e.g., thrombi) from migrating proximally from thepump-outlet tube 24, and also (b) to provide the portion of thepump-outlet tube that defines the blood-outlet openings with arelatively high porosity. Typically, the portion of the pump-outlet tubethat defines the blood-outlet openings has a porosity of more than 40percent, e.g., more than 50 percent, or more than 60 percent (whereporosity is defined as the percentage of the area of this portion thatis porous to blood flow). Thus, on the one hand the blood-outletopenings are relatively small (in order to prevent any elements that aregreater than a given size (e.g., thrombi) from migrating proximally fromthe pump-outlet tube 24), but on the other hand, the porosity of theportion of the pump-outlet tube that defines the blood-outlet openingsis relatively high, such as to allow sufficient blood flow from thepump-outlet tube. The blood-outlet openings as shown in FIG. 15 may beused in combination with any one of the embodiments described herein.For example, the blood-outlet openings as shown in FIG. 15 may be usedas part of a pump-outlet tube that defines a single axially-facingblood-inlet opening 108 (as shown in FIG. 15 ), or it may be used aspart of a pump-outlet tube that defines lateral blood-inlet openings 108(combination not shown).

With regards to all aspects of ventricular assist device 20 describedwith reference to FIGS. 1A-15 , it is noted that, although FIGS. 1A and1B show ventricular assist device 20 in the subject's left ventricle,for some applications, ventricular assist device 20 is placed inside thesubject's right ventricle, such that the device traverses the subject'spulmonary valve, and techniques described herein are applied, mutatismutandis. For some applications, components of device 20 are applicableto different types of blood pumps. For example, aspects of the presentinvention may be applicable to a pump that is used to pump blood fromthe vena cava and/or the right atrium into the right ventricle, from thevena cava and/or the right atrium into the pulmonary artery, and/or fromthe renal veins into the vena cava. Such aspects may include features oftube 24 (e.g., the curvature of the tube), impeller 50, features ofpump-head portion 27, drive cable 130, etc. Alternatively oradditionally, device 20 and/or a portion thereof (e.g., impeller 50,even in the absence of tube 24) is placed inside a different portion ofthe subject's body, in order to assist with the pumping of blood fromthat portion. For example, device 20 and/or a portion thereof (e.g.,impeller 50, even in the absence of tube 24) may be placed in a bloodvessel and may be used to pump blood through the blood vessel. For someapplications, device 20 and/or a portion thereof (e.g., impeller 50,even in the absence of tube 24) is configured to be placed within thesubclavian vein or jugular vein, at junctions of the vein with a lymphduct, and is used to increase flow of lymphatic fluid from the lymphduct into the vein, mutatis mutandis. Since the scope of the presentinvention includes using the apparatus and methods described herein inanatomical locations other than the left ventricle and the aorta, theventricular assist device and/or portions thereof are sometimes referredto herein (in the specification and the claims) as a blood pump.

The scope of the present invention includes combining any of theapparatus and methods described herein with any of the apparatus andmethods described in one or more of the following applications, all ofwhich are incorporated herein by reference:

U.S. Ser. No. 17/609,589 to Tuval, entitled “Ventricular assist device,”which is the US national phase of PCT Application No. PCT/IB2021/052857(published as WO 21/205346), filed Apr. 6, 2021, which claims priorityfrom:

U.S. Provisional Patent Application 63/006,122 to Tuval, entitled“Ventricular assist device,” filed Apr. 7, 2020;

U.S. Provisional Patent Application 63/114,136 to Tuval, entitled“Ventricular assist device,” filed Nov. 16, 2020; and

U.S. Provisional Patent Application 63/129,983 to Tuval, entitled“Ventricular assist device,” filed Dec. 23, 2020.

US 2020/0237981 to Tuval, entitled “Distal tip element for a ventricularassist device,” filed Jan. 23, 2020, which claims priority from:

U.S. Provisional Patent Application 62/796,138 to Tuval, entitled“Ventricular assist device,” filed Jan. 24, 2019;

U.S. Provisional Patent Application 62/851,716 to Tuval, entitled“Ventricular assist device,” filed May 23, 2019;

U.S. Provisional Patent Application 62/870,821 to Tuval, entitled“Ventricular assist device,” filed Jul. 5, 2019; and

U.S. Provisional Patent Application 62/896,026 to Tuval, entitled“Ventricular assist device,” filed Sep. 5, 2019.

US 2019/0209758 to Tuval, which is a continuation of InternationalApplication No. PCT/IB2019/050186 to Tuval (published as WO 19/138350),entitled “Ventricular assist device, filed Jan. 10, 2019, which claimspriority from:

U.S. Provisional Patent Application 62/615,538 to Sohn, entitled“Ventricular assist device,” filed Jan. 10, 2018;

U.S. Provisional Patent Application 62/665,718 to Sohn, entitled“Ventricular assist device,” filed May 2, 2018;

U.S. Provisional Patent Application 62/681,868 to Tuval, entitled“Ventricular assist device,” filed Jun. 7, 2018; and

U.S. Provisional Patent Application 62/727,605 to Tuval, entitled“Ventricular assist device,” filed Sep. 6, 2018;

US 2019/0269840 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2017/051273 to Tuval (publishedas WO 18/096531), filed Nov. 21, 2017, entitled “Blood pumps,” whichclaims priority from U.S. Provisional Patent Application 62/425,814 toTuval, filed Nov. 23, 2016;

US 2019/0175806 to Tuval, which is a continuation of InternationalApplication No. PCT/IL2017/051158 to Tuval (published as WO 18/078615),entitled “Ventricular assist device,” filed Oct. 23, 2017, which claimspriority from U.S. 62/412,631 to Tuval filed Oct. 25, 2016, and U.S.62/543,540 to Tuval, filed Aug. 10, 2017;

US 2019/0239998 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2017/051092 to Tuval (publishedas WO 18/061002), filed Sep. 28, 2017, entitled “Blood vessel tube,”which claims priority from U.S. Provisional Patent Application62/401,403 to Tuval, filed Sep. 29, 2016;

US 2018/0169313 to Schwammenthal, which is the US national phase ofInternational Patent Application PCT/IL2016/050525 to Schwammenthal(published as WO 16/185473), filed May 18, 2016, entitled “Blood pump,”which claims priority from US Provisional Patent Application 62/162,881to Schwammenthal, filed May 18, 2015, entitled “Blood pump;”

US 2017/0100527 to Schwammenthal, which is the US national phase ofInternational Patent Application PCT/IL2015/050532 to Schwammenthal(published as WO 15/177793), filed May 19, 2015, entitled “Blood pump,”which claims priority from U.S. Provisional Patent Application62/000,192 to Schwammenthal, filed May 19, 2014, entitled “Blood pump;”

U.S. Pat. No. 10,039,874 to Schwammenthal, which is the US nationalphase of International Patent Application PCT/IL2014/050289 toSchwammenthal (published as WO 14/141284), filed Mar. 13, 2014, entitled“Renal pump,” which claims priority from (a) U.S. Provisional PatentApplication 61/779,803 to Schwammenthal, filed Mar. 13, 2013, entitled“Renal pump,” and (b) U.S. Provisional Patent Application 61/914,475 toSchwammenthal, filed Dec. 11, 2013, entitled “Renal pump;”

U.S. Pat. No. 9,764,113 to Tuval, issued Sep. 19, 2017, entitled “Curvedcatheter,” which claims priority from U.S. Provisional PatentApplication 61/914,470 to Tuval, filed Dec. 11, 2013, entitled “Curvedcatheter;” and

U.S. Pat. No. 9,597,205 to Tuval, which is the US national phase ofInternational Patent Application PCT/IL2013/050495 to Tuval (publishedas WO 13/183060), filed Jun. 6, 2013, entitled “Prosthetic renal valve,”which claims priority from U.S. Provisional Patent Application61/656,244 to Tuval, filed Jun. 6, 2012, entitled “Prosthetic renalvalve.”

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

1. An apparatus, comprising: a left-ventricular assist device comprising: an impeller configured to be placed inside a left ventricle of a subject and to pump blood from the left ventricle to an aorta of the subject, by rotating; a frame disposed around the impeller; and a pump-outlet tube configured to traverse an aortic valve of the subject, such that a proximal portion of the tube is disposed within the subject's aorta and a distal portion of the pump-outlet tube is disposed within the subject's left ventricle, the distal portion of the pump-outlet tube extending to a distal end of the frame and defining more than 10 blood-inlet openings that are sized such as (a) to allow blood to flow from the subject's left ventricle into the tube and (b) to block structures from the subject's left ventricle from entering into the frame, wherein a porosity of the distal portion of the pump-outlet tube, which defines the blood-inlet openings, is lower within a proximal region of the distal portion of the pump-outlet tube than within a distal region of the distal portion of the pump-outlet tube that is distal to the proximal region.
 2. The apparatus according to claim 1, wherein each of the blood-inlet openings is shaped such that, in at least one direction, a width of the opening is less than 1 mm.
 3. The apparatus according to claim 1, wherein a ratio of the porosity of the distal portion of the pump-outlet tube within the distal region to the porosity of the distal portion of the pump-outlet tube within the proximal region is more than 4:3.
 4. The apparatus according to claim 1, wherein the porosity of the distal portion of the pump-outlet tube is varied between the proximal region and the distal region such as to account for varying blood flow dynamics at different regions of the distal portion of the pump-outlet tube.
 5. The apparatus according to claim 1, wherein the distal portion of the pump-outlet tube is conical, and wherein the porosity of the distal portion of the pump-outlet tube is varied between the proximal region and the distal region such as to account for changes in the shape of the distal conical portion along its length.
 6. The apparatus according to claim 1, wherein along the distal region of the distal portion of the pump-outlet tube, the pump-outlet tube defines large blood-inlet openings that are configured to reduce a risk of thrombosis relative to if the blood-inlet openings along the distal region of the distal conical portion of the pump-outlet tube were smaller.
 7. The apparatus according to claim 1, wherein the distal portion of the pump-outlet tube defines more than 50 blood-inlet openings that are sized such as (a) to allow blood to flow from the subject's left ventricle into the tube and (b) to block structures from the subject's left ventricle from entering into the frame.
 8. The apparatus according to claim 1, wherein the blood-inlet openings are rectangular and are shaped such that a ratio of lengths to widths of each of the blood-inlet openings is between 1.1:1 and 4:1.
 9. The apparatus according to claim 1, wherein the blood inlet openings are rectangular and are shaped such that a ratio of lengths to widths of each of the blood-inlet openings is between 3:2 and 5:2.
 10. The apparatus according to claim 1, wherein the distal portion of the pump-outlet tube has a porosity of more than 40 percent.
 11. The apparatus according to claim 10, wherein the distal portion of the pump-outlet tube has a porosity of more than 50 percent.
 12. The apparatus according to claim 11, wherein the distal portion of the pump-outlet tube has a porosity of more than 60 percent.
 13. The apparatus according to claim 1, wherein the frame defines a central cylindrical portion and a distal conical portion, wherein the distal portion of the pump-outlet tube, which defines the blood-inlet openings, is conical and is disposed over the distal conical portion of the frame, and wherein a portion of the pump-outlet tube that is proximal to the distal portion of the pump-outlet tube is coupled to the central cylindrical portion of the frame.
 14. The apparatus according to claim 13, wherein the portion of the pump-outlet tube that is proximal to the distal portion of the pump-outlet tube is coupled to the central cylindrical portion of the frame via heating, and wherein the porosity is lower is within the proximal region of the distal portion of the pump-outlet tube, such that damage that may be caused to a material that defines the blood-inlet holes within the proximal region of the distal portion of the pump-outlet tube is reduced during the heating relative to if the porosity within the proximal region of the distal portion of the pump-outlet tube was higher.
 15. The apparatus according to claim 13, further comprising an inner lining coupled to an inner surface of the central cylindrical portion of the frame, such that the inner lining provides the central cylindrical portion of the frame with a smooth inner surface.
 16. The apparatus according to claim 13, wherein the proximal region of the distal portion of the pump-outlet tube extends along a length of 0.5-2 mm.
 17. The apparatus according to claim 1, wherein the blood-inlet openings have polygonal shapes.
 18. The apparatus according to claim 17, wherein the blood-inlet openings have hexagonal shapes.
 19. The apparatus according to claim 17, wherein, within the proximal region of the distal portion of the pump-outlet tube, a diameter of a circle enclosed by each of the blood-inlet openings is between 0.1 and 0.6 mm.
 20. The apparatus according to claim 17, wherein, within the proximal region of the distal portion of the pump-outlet tube, widths of gaps between adjacent blood-inlet openings are between 0.05 and 0.2 mm.
 21. The apparatus according to claim 17, wherein, within the distal region of the distal portion of the pump-outlet tube, a diameter of a circle enclosed by each of the blood-inlet openings is between 0.2 and 0.8 mm.
 22. The apparatus according to claim 17, wherein, within the distal region of the distal portion of the pump-outlet tube, widths of gaps between adjacent blood-inlet openings are between 0.01 mm and 0.1 mm.
 23. The apparatus according to claim 17, wherein a ratio of a diameter of a circle enclosed by each the blood-inlet openings with the distal region of the distal portion of the pump-outlet tube to a diameter of a circle enclosed by each of the blood-inlet openings with the proximal region of the distal portion of the pump-outlet tube is greater than 7:6.
 24. The apparatus according to claim 17, wherein a ratio of widths of gaps between adjacent blood-inlet openings with the proximal region of the proximal portion of the pump-outlet tube to widths of gaps between adjacent blood-inlet openings within the distal region of the distal portion of the pump-outlet tube is greater than 3:2. 